Low Profile Dual Locking Fixation System and Offset Anchor Member

ABSTRACT

A coupling device for securing an elongate member to the spine is provided. The coupling device comprises a compressible inner member that secures an anchor member therein when the inner member is axially shifted within an outer member. The elongate member is retained within the device by an axially inserted locking member, and may be secured independently of the anchor member. The coupling device and anchor may be configured to provide increased angulation of the anchor with respect to the coupling device. For instance, anchor member may have an offset head portion in order to provide normal pivoting of the coupling device when the anchor is attached to bone at an angle.

RELATED APPLICATIONS

This application is a non-provisional application claiming the benefitof U.S. Provisional Applications 61/105,047 filed Oct. 14, 2008 and61/105,048 filed Oct. 14, 2008, both of which are hereby incorporated byreference as if fully set forth herein.

FIELD OF THE INVENTION

The present systems and methods relate to bone fixation devices. Moreparticularly, the present systems and methods provide for a low profilescrew assembly configured to facilitate the internal fixation ofvertebral bodies.

BACKGROUND OF THE INVENTION

Various devices for internal fixation of bone segments in the human oranimal body are known in the art. For instance, pedicle screw and/orhook systems are sometimes used as an adjunct to spinal fusion surgery.Such systems may have a rod-receiving portion and an integral anchorportion, or may be provided with a separate anchor member, especiallyone that may be pivoted with respect to a rod-receiving member. Althoughpedicle screw systems, comprising a pedicle screw and a rod-receivingdevice, are commonly used, it is also possible to anchor a rod-receivingdevice to the spine with a different type of anchor member, such as alaminar hook. The pedicle screw portion of such a system includes anexternally threaded stem and a head portion. The rod-receiving device(also referred to as a coupling device) couples the pedicle screw to aspinal rod by receiving and fixing the head portion of the pedicle screwand the elongate spinal rod (commonly referred to as a distraction rod).Two such systems are inserted into respective vertebrae and adjustedalong the spinal rod to distract, de-rotate, and/or stabilize a spinalcolumn, for instance to correct scoliosis or stabilize the spinal columnin conjunction with an operation to correct a herniated disk. Thepedicle screw does not, by itself, fix the spinal segment, but insteadoperates as an anchor point to fix the coupling device relative to thespinal segment into which the pedicle screw is driven, with the couplingdevice in turn receiving the rod extending therethrough. One goal ofsuch a system is to substantially reduce and/or prevent relative motionbetween the spinal segments that are being fused.

Known pedicle screw systems have several drawbacks. For instance, somepedicle screw systems include rather large and bulky assemblies tosecure a rod, thus increasing opportunities for tissue damage in andaround the surgical site during installation. Many devices are alsodifficult to assemble and/or install. These problems become even moresignificant when implanting a coupling member and anchor member intosmaller portions of the spine, such as the cervical vertebrae. Forinstance, installation of coupling members into adjacent cervicalvertebrae often requires the central axis of the anchor member andcoupling member of polyaxial pedicle screw systems to be pivoted to moreextreme angles relative to each other than required in other vertebralregions, due to the size, proximity, and curvature of the vertebrae inthe cervical spine.

SUMMARY OF THE INVENTION

In one aspect, low profile coupling devices for coupling an elongatemember, such as a spinal rod, to one or more anchor members attached tovertebrae are provided herein. The anchor member may include a screw,hook, or other bone fixation device for securing implants to bone.Although the anchor member may be formed integrally with the inner orouter member, it is preferably provided as a separate structure and morepreferably pivotably received in the coupling device to allow thecoupling device to be fixed at various angles with respect to theanchor. This may be accomplished by providing the anchor with anenlarged, spherical or partially spherical head portion that is seatedwithin the coupling device while a narrower shank portion of the anchormember extends outwardly from the coupling device through a passage inthe device. In one form, the degree to which the anchor may be pivotedwith respect to the coupling member may be increased by having the headportion of the anchor be offset from the shank portion or otherwisepositioning the head portion of the anchor so that it is offset from theshank portion axis, so that when the head portion is in a neutralposition in the coupling device the anchor shank can be pivoted indirections generally toward the offset head by a larger amount thanotherwise would be possible if the anchor head and shank were aligned.The offset anchor head and shank are arranged such that the anchor headhas a central axis that is offset from and extends generally parallel tothe longitudinal axis of the shank of the anchor member so that when theanchor head is seated in the coupling device so that its central axisextends along the central axis of the coupling device, the longitudinalaxis of the shank will be offset from the coupling device axis.

The rod-receiving or coupling device may be of many differentconfigurations. For instance, in one form the coupling device has anouter member, an insert member for being received in the outer member,and a rod retaining member for securing the rod within the insert and/orouter members. If the anchor member is received in the inner member, theinner member includes at least one flexible portion that is shiftedagainst the anchor member during linear shifting of the insert memberrelative to the outer member. A linearly inserted rod retaining member,such as a locking cap, interacts with the insert and/or outer members toshift a portion of the inner member against the elongate member, fixingthe elongate member with respect to the coupling device. The assemblymay be configured for independent locking of the anchor member andelongate member, so that one may be secured to the assembly before theother. For instance, the anchor member may be received within a lowerportion of the insert member and secured therein by linear shifting ofthe insert member relative to the outer member, while the elongatemember is received in an upper seat portion of the insert member andsecured by linearly inserting the rod retaining member into engagementwith the upper portion of the insert member.

An exemplary coupling device configured to couple a spinal rod to thehead of a bone anchor includes a generally cylindrical insert axiallyreceived in an interior space of an annular outer member to form atulip-shaped assembly. The insert member may include a lower portionwith a generally spherical cavity configured to receive the head of ananchor member and an upper portion having a rod-receiving channel orseat. According to one exemplary embodiment, flexible, upstanding,laterally-spaced arms are arranged on either side of the channel and areconfigured to provisionally couple an elongate member by resilientlydeflecting to grip a rod placed in the channel. The exemplary couplingassembly also includes an outer member or body having a bore, with atleast a portion of the bore sized and configured to compress the insertmember. After the head of the anchor member is received in the lowerportion of the insert member, the outer member may be moved over theouter surface of the insert member, compressing the insert member tocompressibly lock its lower portion onto the bone fixation device.Moreover, a rod retaining device engages the insert member and applies acompressive force radially toward the rod to secure the position of therod. For instance, the rod retaining device may be provided in the formof a cap with at least one depending leg configured for friction fittingbetween the insert member and the outer member. Preferably, projectionsfrom the cap are wedged between an upper portion of the insert memberand the outer member, deflecting one or more flexible portions of theinsert member toward the rod and applying a compressive locking forcethereto. This locking force is transverse to the axis of the anchormember and the axis of the coupling assembly, so that little or no capstructure need be provided above the rod, thus minimizing the height ofthe assembly.

In one form, the insert member may have a lower annular wall that formsa cavity or orifice configured for pivotably receiving the head of thebone fixation device therein, and one or more axial slits or gaps thatextend through the annular wall to provide the annular wall withflexibility, allowing for expansion of the cavity. In such anarrangement, the anchor member may be snap-locked into the cavity of theinsert member by deflecting portions of the annular wall to temporarilywiden the opening to the interior cavity. Preferably, the snap-lock fitmay apply a light compressive force onto the head of the anchor memberso that the insert member may be positioned about the anchor head andthen released with the frictional force between the wall lower surfaceand the anchor head being sufficient to retain the insert member at adesired orientation relative to the anchor member. However, thesnap-lock fit may instead loosely retain the head without significantfriction. The head may also be loosely received in the insert memberwithout snap-locking.

The outer member has an interior space in the form of a through openingin which the insert member is received. In one form, the opening throughthe outer member may comprise at least one radially narrow portion andat least one radially wide portion, with the wide portion sized andconfigured to allow expansion of the insert member when located therein,and the narrow portion sized and configured to exert a radialcompressive force upon the insert member. In such an embodiment, thehead of the anchor member may be received by the insert member via asnap-lock fit when the insert member is located within the wide portionof the outer member in a substantially non-compressed configuration.Alternatively, substantially the entire space may be sized so that thewalls exert a radial compressive force upon the insert member insertedtherein, or one or more protrusions in the space may be configured tocompress the insert member. The wall of the insert may also have astepped configuration wherein wall portions are concentrically narrowedfrom top to bottom so that downward shifting of the insert member intothe outer member sequentially achieves different stages of locking thatapply different amounts of predetermined frictional force upon theanchor head.

The insert member and/or outer member may include one or moreprotrusions, recesses, or other structures to substantially prevent theinsert member from unintentional separation from the outer member orbacking out of the inner space of the outer member once inserted. Thishelps to prevent disengagement of the anchor member from the insertmember while the assembly is manipulated under significant force, forinstance during rotation of the vertebrae so that the device may receivethe elongate member. The head of the anchor member may also beconfigured so that it may be shifted to multiple orientations within theinsert member, at least one orientation reducing forces that expand thelower portion of the insert member in order to more securely retain thehead within the tulip assembly.

An apparatus and method also are disclosed for the making and use of areducer inserter tool for use with the disclosed coupling devices. Thereducer/inserter tool is generally applicable to surgical instrumentsbut is particularly suited to locking a spinal rod and cap onto a screwassembly, such as the screw assemblies described above or in U.S. PatentApplication No. 2007/0225711, wherein an outer member, insert member,anchor member, and rod lock member or cap are all linearly (axially)assembled and locked together through axial movement to fix the anchormember and rod in place. The reducer inserter tool consists of threecannulated shafts shiftable within one another. The outer shaftfunctions as an exterior housing, and a hollow reducer shaft assembly orsleeve disposed concentrically within the outer shaft functions toreduce a rod (shift the rod into engagement with a screw assembly). Aninner drive shaft disposed concentrically within the reducer shaftfunctions to drive a cap or other rod locking member into the couplingassembly to lock the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various exemplary embodiments ofsystems and methods for securing an elongate member to the spine and area part of the specification. Together with the following description,the drawings demonstrate and explain the principles of the systems andmethods. The illustrated embodiments are examples of the systems andmethods and do not limit the scope thereof.

FIGS. 1A and 1B are an axial view and a transverse view, respectively,of a spinal rod coupled to an exemplary assembled pedicle screw systemhaving a rigid outer member and compressible insert member.

FIG. 2 is an exploded axial view of a spinal rod and a pedicle screwsystem having a rigid outer member and compressible insert member.

FIG. 3 is a perspective view of a pedicle screw.

FIG. 4 is a front exploded view of a coupling assembly of the pediclescrew system of FIG. 1, according to one exemplary embodiment.

FIG. 5 is a side exploded view of a coupling assembly of the pediclescrew system of FIG. 1, according to one exemplary embodiment.

FIG. 6 is a front exploded cross-sectional side view of the pediclescrew system of FIG. 4, according to one exemplary embodiment.

FIGS. 7A-7D are front, side, front cross-sectional, and cut-awayperspective views, respectively, of an outer member of a couplingassembly, according to one exemplary embodiment.

FIGS. 8A-8D are front, side, and cut-away perspective views,respectively, of an insert member, according to one exemplaryembodiment.

FIGS. 9A-9C are front, side, and cut-away perspective views,respectively, of a compression cap, according to one exemplaryembodiment.

FIG. 10 is a flow chart illustrating a method for securing an axiallylocking coupling assembly on a pedicle screw, according to one exemplaryembodiment.

FIGS. 11A and 11B are an exploded front view and a cross-sectionalperspective view, respectively, of the components of a pedicle screwsystem prior to assembly, according to one exemplary embodiment.

FIGS. 12A and 12B are an exploded front view and a cross-sectionalperspective view, respectively, of the components of the pedicle screwsystem of FIG. 10 with the assembly coupled to a head of a pediclescrew, according to one exemplary embodiment.

FIGS. 13A and 13B are a front view and a cross-sectional perspectiveview, respectively, of the components of the pedicle screw system ofFIG. 10 as a rod is snapped into the insert member, according to oneexemplary embodiment.

FIGS. 14A and 14B are a front view and a cross-sectional perspectiveview, respectively, of the components of a pedicle screw system duringprovisional lock of the assembly with respect to the pedicle screw,according to one exemplary embodiment.

FIGS. 15A and 15B are a front view and a cross-sectional perspectiveview, respectively, of the components of a low top pedicle screw systemas a compression cap is snapped into place, according to one exemplaryembodiment.

FIGS. 16A and 16B are a front view and a cross-sectional front view,respectively, of the components of a pedicle screw system in a fullyassembled position, according to one exemplary embodiment.

FIG. 17 is a perspective view of one exemplary embodiment of an insertmember with retention features to limit axial shifting of the insertmember with respect to an outer member.

FIG. 18 is a perspective view of an exemplary embodiment of an outermember with inwardly-facing retention features and with bores in itsside surfaces for receiving an instrument.

FIGS. 19A and 19B are a front view and a front cross-sectional view,respectively, of the coupling assembly of FIGS. 17 and 18, and retentionfeatures thereof, in a screw-receiving configuration.

FIGS. 20A and 20B are a front view and a front cross-sectional view,respectively, of the coupling assembly of FIGS. 17-19 in ascrew-retaining configuration.

FIGS. 21A and 21B are a front view and a front cross-sectional view,respectively, of the coupling assembly of FIGS. 17-20 in a screw-lockingconfiguration.

FIGS. 22A-22C are perspective views of an exemplary alternative boneanchor in the form of a pedicle screw having a truncated spherical headportion.

FIGS. 23A and 23B are a perspective and bottom plan view, respectively,of an exemplary insert member configured to receive the alternative boneanchor of FIG. 22.

FIGS. 24A-24C depict insertion and retention of the bone anchor of FIG.22 in the insert member of FIG. 23.

FIGS. 25A and 25B are top plan views of the insert member of FIGS. 23-24demonstrating rotation of the bone anchor from FIG. 22 therein from aninsertion position to a retention position.

FIG. 26 is a perspective view of another exemplary polyaxial couplingassembly showing a coupling device having a shaft of an anchor memberprojecting out therefrom offset from the enlarged head portion in thecoupling device.

FIG. 27 is an exploded perspective view of the coupling assembly of FIG.26.

FIGS. 28A and 28B are side elevational and perspective views,respectively, of the pedicle screw anchor member showing the respectiveoffset axes of the head portion and shank portion thereof.

FIG. 29 shows a coupling assembly mounted to a vertebra.

FIGS. 30A and 30B are top and bottom isometric views of an insert memberor core member of a coupling assembly.

FIGS. 30C and 30D are front and side cross-sectional views,respectively, of the offset head of the pedicle screw member received ina core member of the coupling assembly.

FIGS. 31A and 31B are isometric and cross-sectional views, respectively,of an outer member or yoke of the coupling assembly.

FIGS. 32A-D are front and cross-sectional views demonstrating locking ofan exemplary coupling assembly.

FIG. 33 is a perspective view of another exemplary coupling assemblyincluding the anchor member having offset head and shank portions.

FIG. 34 is an exploded perspective view of the coupling assembly of FIG.33.

FIG. 35 is a cross-sectional view of the coupling assembly of FIG. 33.

FIG. 36 is an isometric view of an insert member of the couplingassembly of FIG. 33.

FIGS. 37A, 37B, and 37C are front, upper isometric, and lower isometricviews, respectively, of a cap member for coupling assembly of FIG. 33.

FIG. 38 is a front view of an additional embodiment of a couplingassembly.

FIG. 39 is a cross-sectional view of the coupling assembly of FIG. 38.

FIG. 40 is a cross-sectional view of the coupling assembly of FIG. 38when fully locked.

FIG. 41 is a perspective view of the coupling assembly of FIG. 38 withthe cap removed.

FIG. 42 is an elevational view of a screw inserter tool with an offsetinterface portion for engaging the offset head portion of the anchormember of FIGS. 28A and 28B.

FIG. 43 is an elevational view of the screw inserter of FIG. 42interfacing with the offset screw head.

FIGS. 44A and 44B are perspective and exploded views, respectively, of atransverse connector device.

FIG. 45 is a front plan view of a transverse connector device.

FIGS. 46-47 are front cross-sectional views of a transverse connectordevice in a compact configuration and an extended configuration,respectively.

FIGS. 48A-B are perspective views of a reducer/inserter tool for lockinga coupling device.

FIG. 49 is an exploded perspective view of the reducer/inserter tool.

FIG. 50 is a cross-sectional view of the reducer/inserter tool.

FIG. 51A-B are detailed cross-sectional views of the head portion of thereducer inserter tool.

FIG. 52 is a detailed cross-sectional view of the cap driving mechanismof the reducer/inserter tool.

Throughout the drawings, identical reference numbers designate similarbut not necessarily identical elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-43 illustrate systems and methods for locking the orientation ofan anchor member and elongate member with respect to a first type ofcoupling assembly, sometimes referred to as a “tulip assembly,” in whichan insert member is inserted linearly into a space within an outermember. Axial shifting of the outer member and insert relative to oneanother (and the consequent radial compression exerted thereby) locksthe position of the coupling assembly relative to an anchor member orfixation device (e.g. a pedicle screw or hook). Further, according toone exemplary embodiment, a coupling assembly may be configured to beplaced on the head of a polyaxial pedicle screw after placement of thepedicle screw in a patient's body and configured to receive andpositionally secure a top loaded rod. Further details of the presentexemplary system and method will be provided below.

By way of example, pedicle screw systems may be fixed in the spine in aposterior lumbar fusion process via minimally invasive surgery (MIS)techniques. The systems are inserted into the pedicles of the spine andthen interconnected with rods to manipulate (e.g., correct thecurvature, compress or expand, and/or structurally reinforce) at leastportions of the spine. Using the MIS approach to spinal fixation and/orcorrection surgery, in which implantation and manipulation of the systemare accomplished through relatively small openings, has been shown todecrease a patient's recovery time and reduce the risks of follow-upsurgeries.

The ability to efficiently perform spinal fixation and/or correctionsurgeries using MIS techniques is enhanced by the use of pedicle screwsystems provided in accordance with the present exemplary systems andmethods, which systems and methods provide a number of advantages overconventional systems. For example, a pedicle screw system in accordancewith one embodiment of the present exemplary system and method providesthe advantage that the pedicle screw (or other type of anchor member)may be inserted into the bone without being pre-operatively coupled withthe coupling assembly. This is advantageous because the surgeon oftenneeds to do other inter-body work after inserting the pedicle screw, butbefore attaching the larger and bulkier coupling assembly. This alsoallows the fixation device to be positioned within the body and securedto the spine without the assembly obscuring the surgeon's view orcontact with the pedicle screw. Such an advantageous pedicle screwsystem may be even more crucial when using MIS techniques because theinter-body spatial boundaries in which the surgeon must work may bequite limited.

In addition, pedicle screw systems in accordance with severalembodiments of the present system and method advantageously allow a userto fix (e.g., lock) the coupling assembly to the pedicle screw at adesired angle either before or after inserting and/or capturing the rod.Fixing or locking the coupling assembly to the pedicle screw means thatat least one of the components of the coupling assembly is manipulatedto grip and/or clamp onto the pedicle screw to reduce and/or prevent anytranslational and/or rotational movement of the coupling assemblyrelative to the pedicle screw. In fact, the assembly may be configuredto have both provisional screw lock and final screw lock positions, sothat in the provisional screw lock position or positions the couplingassembly grips the screw head with sufficient force to maintain aselected angulation of the assembly with respect to the screw unlessforce is applied by hand or instrument to change said angulation,whereas the final screw lock position applies a greater force to thescrew head than the provisional lock and maintains the assembly at aselected angulation with respect to the screw with sufficient force toprevent movement thereof under physiological loads generated by thebody. The ability to lock the coupling assembly to the pedicle screwprior to placing the rod into the coupling assembly may facilitate thesurgeon in performing compression and/or distraction of various spinaland/or bone sections.

Similarly, the assembly may have provisional rod locking positions forloosely retaining the rod so that it is coupled to the assembly but maystill be manipulated (e.g. shifted or rotated) therein prior to full rodlocking.

The term “distraction,” when used herein and when used in a medicalsense, generally relates to joint surfaces and suggests that the jointsurfaces move perpendicular to one another. However when “traction”and/or “distraction” is performed, for example on spinal sections, thespinal sections may move relative to one another through a combinationof distraction and gliding, and/or other degrees of freedom.

Another advantageous feature of at least one embodiment of the presentexemplary system and method is that the complete coupling assembly canbe coupled to the head portion of the pedicle screw intra-operatively.This advantageous coupling assembly may include aspects or features thatenable the coupling assembly to be provisionally or fully locked ontothe head portion of the pedicle screw and then to further receive,capture, and finally lock the rod into the coupling assembly. Thisadvantageous coupling assembly may decrease the complexity of thepedicle screw system installation by reducing the installation toessentially a three-step process including: inserting the pedicle screwinto bone, coupling and/or locking the coupling assembly to the pediclescrew, which may be accomplished with or without the rod in the couplingassembly, and then locking the rod into the coupling assembly. However,the system need not be installed following these steps in theaforementioned order. For instance, the coupling assembly may be coupledto the pedicle screw, and even provisionally and/or finally locked tothe screw, prior to implantation of the screw into bone so that thescrew and coupling assembly are implanted simultaneously. Furthermore,the screw locking and rod locking steps may be accomplishedsimultaneously rather than as separate steps. In addition toaccommodating the MIS approach to spinal correction and/or fusion, thepresent exemplary systems and methods are configured to eliminateinstances of cross-threading and/or post-operative splaying of theassembly, which may be caused by forces exerted by postoperative backflexion that open the coupling assembly and eventually lead to thedisassembly and/or the failure of the pedicle screw system.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present system and method for providing a low toppedicle screw coupling system that is capable of separately locking theorientation of a coupling assembly relative to a pedicle screw and apositional location of a rod in the coupling assembly. It will beapparent, however, to one skilled in the art that the present method maybe practiced without these specific details. Reference in thespecification to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment. Theappearance of the phrase “in one embodiment” in various places in thespecification are not necessarily all referring to the same embodiment.

Exemplary Overall Structure of FIGS. 1-16

While the present system and method may be practiced by or incorporatedinto any number of bone fixation systems, the present system and methodwill be described herein, for ease of explanation only, in the contextof a pedicle screw system. Accordingly, the present system and methodincludes, according to one exemplary embodiment illustrated in FIGS. 1Aand 1B, a low top pedicle screw system 100 including a pedicle screw102, a rod 104, and a rod-receiving assembly or coupling assembly 106(sometimes referred to as a tulip assembly) including a low profile rodlock member such as a compression cap 108. According to one exemplaryembodiment of the present system and method, the coupling assembly 106is configured to separately lock the orientation of the couplingassembly 106 relative to the pedicle screw 102 and the positionallocation of the rod 104 in the coupling assembly 106. Operation of thecoupling assembly 106 as well as its interaction with both the pediclescrew 102 and the rod 104 will be described in further detail below withreference to the Figures.

According to one exemplary embodiment, FIGS. 1A and 1B generally show apedicle screw system 100 comprising a pedicle screw 102, a rod 104, anda coupling assembly 106, hereinafter referred to as a coupling assembly106. As illustrated in FIG. 1, the pedicle screw system 100 isconfigured to securely couple the coupling assembly 106 to the head 110of the pedicle screw 102, thereby locking or fixing the couplingassembly 106 in an angular position relative to the pedicle screw 102.Additionally, as shown in FIGS. 1A and 1B, the present exemplary pediclescrew system 100 is configured to receive a rod 104 and positionally fixthe rod 104 in the coupling assembly 106.

FIG. 2 illustrates an exploded view of the present low top pedicle screwsystem 100, according to one exemplary embodiment. As illustrated inFIG. 2, the coupling assembly 106 of the low top pedicle screw system100 includes a number of components configured to perform theabove-mentioned angular and positional fixing including, but in no waylimited to, an outer member or yoke 450, an insert member or core member400, and a compression cap 108. According to one exemplary embodiment,the coupling assembly 106 including the insert member 400 is configuredfor insertion into the outer member and further configured to engage thehead portion 110 of the pedicle screw 102, as described in furtherdetail below. Moreover, the coupling assembly 106 in connection with thecompression cap 108 is configured to securely couple the rod 104 to theassembly. Detailed descriptions of each component of the present low toppedicle screw system 100 will be described in further detail below, withreference to FIGS. 3 through 9B.

FIG. 3 further illustrates the components of a pedicle screw 102,according to one exemplary embodiment. As illustrated in FIG. 3, thepedicle screw 102 includes an elongated, threaded portion 108 and a headportion 110. Although pedicle screws are generally known in the art, thehead portions may be of varying configurations depending on what type ofcoupling assembly is to be coupled to the pedicle screw. The headportion 110 of the present exemplary pedicle screw 102 includes adriving feature 124 and a maximum diameter portion 126. The drivingfeature or recess 124 of the present exemplary pedicle screw 102 permitsthe screw to be inserted and rotated into a pedicle bone and/or otherbone. The pedicle bone is a part of a vertebra that connects the laminawith a vertebral body. Additionally, according to the present exemplaryembodiment, the driving feature 124 can be used to adjust the pediclescrew 102 prior to or after the coupling assembly 106 is coupled to thepedicle screw 102. In the illustrated embodiment, the head portion 110of the pedicle screw 102 is coupled to the threaded portion 108 andincludes a generally spherical surface 127 with a truncated or flat topsurface 128.

In one exemplary embodiment, the pedicle screw 102 is cannulated, whichmeans a channel 130 (shown in dashed lines and extending axially throughthe pedicle screw 102) extends through the entire length of the pediclescrew 102. The channel 130 allows the pedicle screw 102 to be maneuveredover and receive a Kirschner wire, commonly referred to as a K-wire (notshown). The K-wire is typically pre-positioned using imaging techniques,for example, fluoroscopy imaging, and then used to provide preciseplacement of the pedicle screw 102. Numerous variations of the pediclescrew may be made including, but in no way limited to, varying the typeof driving feature 124, varying materials, varying dimensions, and thelike. The screw may also be formed integrally with the coupling assemblyinstead of having a head portion that is pivotably received in aseparate coupling assembly.

Returning again to FIG. 1, the pedicle screw system includes a couplingassembly 106 configured to separately lock the orientation of thecoupling assembly 106 relative to the pedicle screw 102 and thepositional location of the rod 104 within the coupling assembly 106.FIGS. 4, 5, and 6 illustrate the various components of the presentexemplary coupling assembly 106, according to one exemplary embodiment.FIG. 4 illustrates a front (along the axis of a captured spinal rod)exploded view of an exemplary coupling assembly 106, while FIG. 5illustrates an exploded view of the present exemplary coupling assembly106 as viewed from the side (transverse to a captured rod). Furthermore,FIG. 6 provides a front cross-sectional view of the present exemplarycoupling assembly 106. As illustrated in FIGS. 4-6, the presentexemplary coupling assembly 106 includes an outer member or body 450substantially housing an insert member 400. Additionally, a throughbore452 is defined in the center of the coupling assembly 106, through boththe insert and outer members, to provide a driving tool access to thedriving feature 124 in a pedicle screw captured by the couplingassembly. In addition, the throughbore allows a K-wire to be passedthrough the coupling assembly and associated cannulated screw. The outermember 450 also defines a rod recess 455 configured to define anultimate rod position during use.

As shown, the insert member 400 may include a number of functionalfeatures including, but in no way limited to a plurality of spaced apartrod engagement members or arms 410 configured to receive a spinal rod.Additionally, a proximal locking feature 415 and a distal lockingfeature 420 are formed on the outer surface of the insert member 400 inorder to interact with the outer member 450 and selectively capture thehead 110 of a pedicle screw 102. The locking features 415 and 420 shownare formed as annular flanges extending from the lower portion of theinsert member 400. Furthermore, the exemplary illustrated compressioncap 108 includes a plurality of compression protrusions in the form oflegs 480 that cooperate with the insert 400 and outer member 450 to lockthe rod. Consequently, the exemplary configurations of the outer member450, the insert member 400, and the compression cap 108 will each beindependently addressed in detail below.

FIG. 7A illustrates a front view of an outer member 450, FIG. 7Billustrates a side view of the outer member, FIG. 7C illustrates across-sectional view of the outer member, and FIG. 7D illustrates apartial cut-away perspective view of an outer member according to oneexemplary embodiment. As illustrated in FIGS. 7A through 7D, the outermember 450 includes a number of elements that facilitate the ability toseparately lock both the positions of the pedicle screw 102 and a rod104 relative to the coupling assembly 106. According to one exemplaryembodiment illustrated in FIGS. 7A through 7D, the outer member 450includes an internal space 452 in the form of a throughbore, a proximalend 750, a distal end 760, a rod reception recess 455 defined by uprightside walls 700, and a number of internal annular features 722, 724, and726 configured to allow for the selective compression and expansion ofan insert member (FIGS. 4, 8).

According to one exemplary embodiment, the bore 452 is configured topermit assembly of the outer member and insert before being placed ontothe head portion of the pedicle screw. In one embodiment, the insertmember 400 of the coupling assembly may be inserted into the outermember 450 through the bore 452. Once the coupling assembly 106 ispre-operatively assembled, a wide portion of the bore facilitatesreception of the head portion 110 of the pedicle screw 102 within theinsert member 400, as will be described in further detail below.

Continuing with FIGS. 7A through 7D, the outer member 450 is illustratedas a generally cylindrical member having a plurality of side walls 700extending toward the proximal end 750 of the outer member. According toone exemplary embodiment, the plurality of side walls 700 define boththe proximal portion of the thru-bore 452 and the rod recess 455including a rod stop surface 710. The rod stop surface may be contouredto match the outer surface of the rod. In the illustrated embodiment,the proximal portion of the outer member 450 is open to receive a spinalrod. As mentioned, the rod 104 may be inserted into the outer member 132either before or after placement of the coupling assembly 106 on thehead portion 110 of the pedicle screw 102. Initially, the rod 104 isreceived by both the insert member 400 and the outer member 450 via therod recess 455. Consequently, according to one exemplary embodiment, thewidth of the rod recess 455 may be substantially equal to or greaterthan the diameter of a desired rod 104. However, according to otherexemplary embodiments, the rod recess 455 may be slightly narrower thanthe diameter of a desired rod 104 to allow for a slight interference fitduring insertion. Once the rod 104 is received by the outer member 450and the insert member 400 via the rod recess 455 the lateral motion ofthe rod is limited by the sidewalls 700 and/or the upright arms 410 ofthe insert member, and in some embodiments the vertical position of therod may be limited, at least in part, by the rod stop surface 710.

The present exemplary outer member 450 also includes a number ofelements that allow the relative angular position of the couplingassembly 106 to be independently established relative to the pediclescrew 102. Specifically, the internal wall of the outer member 450defining the throughbore 720 can include, according to one exemplaryembodiment, a proximal annular compression feature or locking feature722, a distal annular compression feature or locking feature 726 and anannular expansion groove 724. According to one exemplary embodiment, theproximal and distal annular compression features 722, 726 are configuredto interact with the proximal locking feature 415 and distal lockingfeature 420 (FIG. 4) of the insert member to compress the insert memberabout the head portion of the pedicle screw, thereby fixing the relativeangular position of the coupling assembly relative to the pedicle screw,as will be described below with reference to FIGS. 10 through 16B.Additionally, according to one exemplary embodiment, the annularexpansion groove 724 is configured to permit selective expansion of theinsert member 400 to facilitate reception of the head portion 110 of thepedicle screw 102 when the distal annular locking feature is positionedin the annular groove of the outer member, as will be described indetail below. While the present figures and description describe theinternal compression and expansion features as annular protrusions andrecesses, any number of selectively disjointed, or varying protrusionsor recesses may be used to allow selective expansion and compression ofthe present insert member 400. The exterior of the outer member maycontain features to interact with tools designed to implant and operatethe assembly. For instance, as shown in FIG. 18, an outer member maycontain radially-directed bores or openings so that portions of aninstrument may transversely engage and grip the outer member and be usedto position the outer member during implantation or shifting of theouter member relative to the insert member during locking.

The insert member 400 of one illustrated coupling assembly isillustrated in FIGS. 8A through 8C. As shown by the side axial view ofFIG. 8A, the insert member 400 can generally, according to one exemplaryembodiment, include a main body having a proximal end 850 and a distalend 860. As shown, the main body of the insert member 400 includes aplurality of rod retention members 800 in the form of a pair of uprightarms extending therefrom in a proximal direction. According to oneexemplary embodiment, the arms 800 include a number of rod engagementfeatures in the form of ridges 410 formed on inner surfaces of the arms.According to one exemplary embodiment, the arms 800 are spaced apart aproper distance to receive a desired rod 104 and contact and retain thedesired rod at the ridges 410. As shown in FIG. 8A, an expansion gap 810may be formed in the distal end 860 of the insert member 400 tofacilitate expansion and contraction of the rod retention arms 800.Additionally, as previously mentioned, the insert member 400 can includea proximal locking feature 415 and a distal locking feature 420configured to selectively interact with features of the outer member450, including the proximal annular compression feature 722, the annularexpansion gap 724, and the distal annular compression feature 726.According to one exemplary embodiment, the main body and the rodretention arms of the insert member 400 are sized to be received in thethroughbore 452 of the outer member 450 and then be selectively shiftedwithin the outer member to compress the head portion of a desiredpedicle screw 102, as will be described in more detail below.

Turning now to FIG. 8B, which is a side view of the insert member 400,the body of the insert member defines an expansion gap 810 that beginsat the distal end 860 of the insert member 400 and extends into theupper rod retention arms 800. According to one exemplary embodiment, thelarge expansion gaps 810 defined in the insert member 400 facilitateexpansion of the distal end 860 of the insert member, thereby allowingfor reception of a head portion of a desired pedicle screw 102. As shownin FIG. 8C, the distal end 860 of the insert member 400 defines a screwhead receiving orifice or cavity 820 configured to provide a largesurface area of contact with a received pedicle screw head. As will bedescribed in further detail below, the aforementioned features of theinsert member 400 work in conjunction with the features of the outermember 450 and the compression cap 108 to selectively fix the positionof the present coupling assembly 106 relative to a pedicle screw andindependently receive, capture, and eventually positionally lock a rod104 into the coupling assembly. According to one exemplary embodiment, aforced contraction of the distal end 860 of the insert member 400generates sufficient radial pressure on the head portion 110 of thepedicle screw 102 to lock the relative angular position of the couplingassembly with respect to the pedicle screw.

FIGS. 9A through 9C illustrate one type of rod locking member of thepresent exemplary system and method, a compression cap 108. According toone exemplary embodiment, the compression cap 108 is designed to providea low profile for the assembly (having a minimal amount of materialabove the rod), while preventing post operative assembly splaying.Particularly, as shown in FIGS. 9A through 9C, the compression cap 108includes a top surface 910 and a bottom rod mating surface 920.According to one exemplary embodiment, a plurality of compressionprotrusions in the form of legs 480 extend distally from the bottom rodmating surface 920 of the compression cap 108. According to oneexemplary embodiment, described in further detail below, each of thecompression protrusions 480 are configured to be inserted between therod retention arms 800 of the insert members 400 and the side walls 700of the outer member 450. According to one exemplary embodiment, forcingthe compression protrusions 480 between the rod retention protrusions800 of the insert members 400 (FIG. 8A) and the side walls 700 of theouter member 450 (FIG. 7A) both compresses the arms into contact with acaptured rod 104 and prevents the insert member 400 from splaying postoperatively. As shown in FIGS. 9A and 9B, the most distal portion of thecompression cap legs 480 may include an engagement bevel 900 configuredto facilitate the insertion of the compression protrusions between therod retention protrusions 800 of the insert members 400 and the sidewalls 700 of the outer member 450. In addition, the beveled portions 900may extend laterally outward from the legs 480 to allow the compressioncap 108 to snap-lock into the outer member before the cap is fullyinserted. While a number of traditional rod retention systems includeanti-splaying mechanisms, they are typically bulky and greatly increasethe overall height of the mechanism. In contrast, the presentcompression cap 108 protects against post operative splaying of thesystem while minimally impacting the height of the resulting assembly.That is, the only height of the present coupling assembly 106 above acaptured rod when fully assembled is the distance between the rod matingsurface 920 and the top surface 910 of the compression cap 108, asillustrated in FIG. 9A. Furthermore, the rod locking member could beformed without a top portion to further reduce the profile of theassembly. For instance, a single wedge member or a pair of unconnectedwedge members could be inserted between the outer member and the arms ofthe insert to lock the rod.

Further detail of the function and operation of the present couplingassembly will be described below with reference to FIGS. 10-16B.

Exemplary Implementation and Operation of the Coupling Device Shown inFIGS. 1-16

FIG. 10 illustrates one method for installing an exemplary low toppedicle screw system 100 (FIG. 1). As illustrated in FIG. 10, thepresent exemplary method for installing the low top pedicle screw systemincludes inserting one or more pedicle screws in a patient's spinalsystem (step 1000). Once the one or more pedicle screws are inserted ina patient's spinal system, the coupling assembly (106, FIG. 1) isinstalled over the head of the pedicle screw (step 1010). With thecoupling assembly snapped over the head of the pedicle screw, a rod maybe inserted into the rod recess of the insert member (step 1020) and therelative position of the coupling assembly may be oriented as desiredrelative to the pedicle screw (step 1030). When the desired orientationis established, the coupling assembly position relative to the pediclescrew may be locked by linearly shifting the elements of the systemrelative to one another. The insert member 400, outer member 450, andcompression cap 108 all share a common axis, and may be shifted relativeto one another along the axis. The outer member 450 may be shifted overthe insert member 400 in a first, upward direction, and the compressioncap 108 may be shifted in an opposite direction from the opposite sideof the insert member 400 so that the legs 480 of the compression cap areinserted between the insert member 400 and outer member 450.

By positioning the insert member (step 1040), shifting the insert memberrelative to the outer member, the angular position of the screw relativeto the assembly is fixed. With the coupling assembly position relativeto the pedicle screw established due to the positioning of the insertmember, the compression cap may be snapped into the assembly to blockexit of the rod (step 1050) followed by a complete insertion of thecompression cap for a final lock of the rod (step 1060). Alternatively,the compression cap may be inserted into the assembly as the outermember is pulled up around the insert member, simultaneously locking therod 104 and the screw 102 into place. Further details of each step ofthe present exemplary method will be provided below with reference toFIGS. 11A through 16B.

As illustrated in FIG. 10, the first step of the exemplary method is toinsert one or more pedicle screws in a patient's spinal system (step1000) corresponding to a desired number of pedicle screw systems 100;FIG. 1. The placement and/or number of pedicle screw systems 100 to beused in a patient may be pre-operatively determined based on apre-operative examination of the patient's spinal system usingnon-invasive imaging techniques known in the art, such as x-ray imaging,magnetic resonance imaging (MRI), and/or fluoroscopy imaging, forexample.

With the one or more pedicle screws inserted into a patient's spinalsystem (step 1000), the coupling assembly may be snapped over the headof a previously inserted pedicle screw (step 1010). FIGS. 11A and 11Billustrate the exemplary components prior to installation on an insertedpedicle screw 102. As illustrated, the insert member 400 is in an upposition aligning the distal locking feature 420 of the insert member400 with the annular expansion groove 724 of the outer member 450.According to one exemplary embodiment, this configuration allows for theexpansion of the head receiving orifice 820, thereby facilitating thereception of the head portion 110 of the pedicle screw 102. Morespecifically, according to one exemplary embodiment, the alignment ofthe distal locking feature 420 of the insert member 400 with the annularexpansion groove 724 of the outer member 450 allows the head receivingorifice 820 to expand to a diameter larger than the maximum diameter 126of the pedicle screw head 110.

With the coupling assembly 106 in position, the screw head is snappedinto the head receiving orifice 820, as illustrated in FIGS. 12A and12B. According to one exemplary embodiment, the coupling assembly 106may be intra- operatively (i.e., during surgery) coupled to the headportion 110 of the pedicle screw 102 and may be maneuverable to achievea desired placement, orientation, and/or angular position of thecoupling assembly 106 relative to the pedicle screw 102. Alternatively,the coupling assembly may be coupled to the head of the pedicle screwbefore surgery, or the insert member 400 may be coupled to the pediclescrew before the insert member 400 is coupled to the outer member 450.

According to one exemplary embodiment, when the coupling assembly 106 issnapped onto the head portion 110 of the pedicle screw 102, the headportion 110 of the pedicle screw 102 passes through the thru-bore 452and engages the lower portion of the insert member 400. As the couplingassembly 106 is pushed onto the head portion 110 of the pedicle screw102, the lower portion of the insert member 400 expands, due in part tothe expansion gap 810 and snaps onto the head portion 110. The annularexpansion groove 724 in the lower portion of the outer member 450permits the expansion and contraction of the insert member 400. Once thehead portion 110 of the pedicle screw 102 is received in the headreceiving orifice 820, the insert member 400 compresses about the headportion of the pedicle screw. At this point of the installation method,the coupling assembly 106 may be pivotably coupled to the head portion110 of the pedicle screw 102.

With the coupling assembly snapped over the head of the pedicle screw, arod 104 may be inserted into the rod recess 455 of the insert member(step 1020). According to one exemplary embodiment, the rod 104 can besnapped into the insert member 400 either before or after provisionallocking of the coupling assembly 106. As illustrated in FIGS. 13A and13B, both the outer member 450 and the insert member 400 are aligned toreceive the rod 104. According to one exemplary embodiment, the rodrecess 455 and the insert member 400 are specifically sized to receivethe rod 104 without significant interference. Specifically, the rodretention arms 800 are positioned substantially parallel with the rodrecess 455 such that a clear channel to receive the rod 104 isestablished. During insertion of the rod to the coupling assembly 106,the rod retention arms 800 may expand to receive the rod 104. Once therod 104 is received, the rod engagement ridges 410 of the arms establishadditional points of contact on the rod. This is advantageous because itallows the frictional contact points on the rod 104 to be distributedabout the perimeter of the rod, rather than having minimal contactpoints on the arms. It will be understood that the coupling assembly 106may be fixed to the pedicle screw 102 at various stages of the presentexemplary installation of the pedicle screw system 100. In one exemplaryembodiment, the coupling assembly 106 is fixed onto the pedicle screw102 before the rod 104 is fixed or locked into the coupling assembly. Inanother embodiment, the coupling assembly 106 is fixed onto the pediclescrew 102 contemporaneously as the rod 104 is fixed or locked into thecoupling assembly. For ease of explanation, the present method willcontinue to be described according to the exemplary method illustratedin FIG. 10.

With the rod 104 inserted in the coupling assembly (step 1030, FIG. 10)position of the coupling assembly may be oriented as desired relative tothe pedicle screw (step 1030). Specifically, when the desiredorientation is established, the coupling assembly position relative tothe pedicle screw may be locked by positioning the insert memberrelative to the outer member 450. Locking can be obtained by eitherpulling up on the outer member 450 and/or pushing down on either the rod104 or the insert member 400, as illustrated by the arrows in FIGS. 14Aand 14B. Locking is obtained by shifting of the outer member relative tothe insert member to create an interference fit between the proximallocking feature 415 and the distal locking feature 420 of the insertmember 400 and the proximal annular compression feature 722 and thedistal annular compression feature 726 of the outer member 450,respectively. When these mating features are engaged, the head receivingorifice 820 of the insert is compressed about the head portion 110 ofthe pedicle screw 102.

It is understood that the relative angular position of a first couplingassembly 106 to a first pedicle screw 102 may be different from therelative orientation of other pedicle screw systems located elsewhere ona patient's spine. In general, the relative, angular position of thecoupling assembly 106 to the pedicle screw 102 allows the surgeon toselectively and independently orient and manipulate the couplingassemblies 106 of each pedicle screw system 100 installed into thepatient to achieve and/or optimize the goals of the surgical procedure,which may involve compressing, expanding, distracting, rotating,reinforcing, and/or otherwise correcting an alignment of at least aportion of a patient's spine. According to one exemplary embodiment,when the proximal locking feature 415 and the distal locking feature 420of the insert member 400 are engaged with the proximal annularcompression feature 722 and the distal annular compression feature 726of the outer member 450, respectively, the frictional force exerted onthe head portion 110 of the pedicle screw 102 is maintained, locking theassembly in a desired position with respect to the screw.

With the assembly position relative to the pedicle screw established dueto the positioning of the insert member 400, the compression cap 108 maybe snapped into the assembly to retain the rod (step 1050). Asillustrated in FIGS. 15A and 15B, the compression cap 108 is snappedinto the coupling assembly 106 but is not fully seated. According to oneexemplary embodiment, the partial insertion of the compression cap 108fills in the gap between the rod retention arms 800 of the insert member400 and the outer member 450, preventing the insert member fromexpanding. Consequently, the rod 104 is retained within the insertmember 400 and the outer member 450 by an increased pressure orfrictional force being applied at the interface between the rodengagement ridges 410 and the rod 104.

When the positioning of all of the related components is confirmed,complete insertion of the compression cap 108 may be performed for afinal lock of the rod (step 1060). Particularly, as illustrated in FIGS.16A and 16B, according to one exemplary embodiment, completely seatingthe compression cap 108 compresses the rod retention protrusions 800 ofthe insert member 400 to grip the rod 104. Additionally, according toone exemplary embodiment, the insertion of the compression cap 108 mayprevent the outer member 450 from splaying open under operative andpost-operative dynamic and static loading, for example. Splaying isprevented due to the material that is coupled up and over the rod 104 bythe compression cap 108.

As illustrated in the exemplary embodiment of FIGS. 16A and 16B, whenthe compression cap is fully inserted, the rod 104 is forced intosubstantially full engagement with the insert member 400 and outermember 450, with further downward translation prevented by the rod stop710 of the outer member 450. Consequently, the resistive force exertedagainst the rod 104 increases the frictional resistance provided by therod engagement ridges 410 to prevent the rod from slideably translatingwithin the coupling assembly 106. According to one exemplary embodiment,the insertion of the compression cap 108 may be performed by insertingan instrument over the compression cap and forcing it downward into theassembly.

During operation, the exemplary pedicle screw system as illustrated inFIGS. 1-16B is designed for fixation of bone material and/or bonesegments during a surgical procedure, such as fusing spinal segments inwhich MIS techniques are employed. For example, according to oneexemplary embodiment, pedicle screws with coupling members are insertedinto the pedicles of a patient's spine and then the coupling members areinterconnected with rods to provide support to the spine, allowing forpost-operative fusion of the spinal segments. While the pedicle screwcan be inserted with the coupling assembly coupled with the pediclescrew, one embodiment for the installation of the pedicle screw systemincludes inserting the pedicle screw into the bone and subsequentlycoupling the coupling assembly to the pedicle screw, where such anapproach has advantages over currently known pedicle screw systemassemblies and/or installations.

In addition, various structural features of the pedicle screw system asdescribed, but not limited to the embodiments herein, may provide otheradvantages over existing pedicle screw systems. First, the pedicle screwmay be inserted into the bone of a patient without the presence of thecoupling assembly or rod, which permits the surgeon to place the screwand then perform subsequent inter-body work without having to workaround the coupling assembly or the rod. Second, the coupling assemblyincludes a mechanism for capturing the rod that eliminates problemsassociated with conventional pedicle screws, such as cross-threading,because the exemplary pedicle screw systems disclosed herein do not useany threads or other elements requiring a rotatable cap member to couplethe coupling assembly to the rod and pedicle screw. Third, the interfacebetween the head portion of the pedicle screw and the coupling assemblyprovide an initial lock, which allows the angle of the coupling assemblyto be set or fixed with respect to the pedicle screw before insertion ofthe rod and/or before the rod is captured in the coupling assembly. Withthis type of pedicle screw system, the surgeon has the ability to checkand even double check the placement, angle, and/or orientation regardingaspects of the pedicle screw system to facilitate, and even optimize,the compression, distraction, and/or other manipulation of the spinalsegments. In contrast, many prior art pedicle screw assemblies aredesigned such that a cap member designed to secure the rod in place alsoacts to force the rod downward onto the head of a pedicle screw,clamping the screw head against a bottom surface of the assembly andlocking the position of the screw simultaneously with locking theposition of the rod. A disadvantage of these prior art pedicle screwsystems is that the assembly pivots freely upon the head of the pediclescrew until the rod is secured in the assembly and locked into placeagainst the screw head. In the present system, the cap and outer membermay be shifted simultaneously in order to simultaneously lock the screwand rod into position, but the screw may also be locked into positionprior to the rod being received in the coupling assembly.

One possible post-operative advantage of the present exemplary pediclescrew system is that the cooperation and interaction of the insertmember 400 with the compression cap 108 substantially reduces, and mostlikely prevents, the known problem of the assembly splaying. Assemblysplaying is generally regarded as a post-operative problem caused by astressed rod forcing open portions of the outer member, which eventuallyleads to the disassembly and likely failure of the pedicle screw systemwithin the patient.

Yet another post-operative advantage of the pedicle screw systems isthat unlike existing rod-coupling members or constructs, the exemplarycoupling assemblies described herein have a smaller size envelope (e.g.,are less bulky, have a lower profile, and/or are more compact in shape)and are easier to place onto the pedicle screw when compared totraditional systems. The smaller size and ease of installation mayreduce trauma to the soft-tissue regions in the vicinity of the surgicalsite, which in turn generally allows for a quicker recovery by thepatient. According to aspects described herein, and as appended by theclaims, the present exemplary pedicle screw systems permit insertion ofthe pedicle screw without the coupling assembly coupled thereto, lockingthe coupling assembly onto the pedicle screw, and subsequently capturingand locking the rod into the assembly.

Exemplary Additional Screw Retention Features Illustrated in FIGS. 17-25

In addition to the general structure and function described, andexemplary embodiments thereto, it is desirable in some circumstances toimplement additional features to strengthen the mating relationshipbetween the coupling assembly and the pedicle screw or other anchormember prior to final locking, since after implantation it is oftennecessary to apply significant amounts of force in order to rotate andshift the coupling assemblies into alignment with each other or intoalignment with spinal rods. Retention features may be added to preventthe screw head from escaping the cavity in the lower portion of thecoupling assembly when in a provisional screw lock position prior tofull screw locking, allowing the coupling assembly to be pivoted aboutthe screw head but preventing the screw head from separating from thecoupling assembly.

In one form, the insert member and outer member may be provided withfeatures to limit axial or other linear movement with respect to eachother prior to full locking, allowing for one-way locking of the insertmember and outer member and preventing the insert member from backingout of the outer member once inserted to a predetermined position. Forexample, the embodiment depicted in FIGS. 17-21 has one-way retentionelements in the form of outwardly-extending inclined retention tabs 1403on the insert member 1400 (FIGS. 17A-B) and complementaryinwardly-extending inclined retention tabs 1453 on the outer member 1450(FIG. 18). The outer member retention tabs 1453 are positioned to engagethe inner member retention tabs 1403 when the inner member shiftsaxially within the outer member 1450. As shown in one exemplaryembodiment in 17A, the insert tabs 1403 may protrude from the flexiblearms 1800 of the rod-retaining portion of the insert. In this position,the tabs do not shift inward as portions of the annular wall 1411 of thelower portion flexes, as shown in FIG. 17B, since the flexible arms 1800are transverse to the major expansion gaps 1810 a primarily responsiblefor flexion of the annular wall portions 1411 and expansion of thecavity formed thereby. Minor expansion gaps 1810 b in the annular wall1411 of the insert 1400 have a shorter length in the axial directionthan the major expansion gaps, and therefore do not provide for the sameamount of flexion of the annular wall 1411 as the major expansion gaps1810 a.

The insert 1400 is shown in FIGS. 19A-B in an initial position withinthe internal space of the outer member 1450, wherein the retention tabs1403 on the insert and retention tabs 1453 on the outer member do notinterfere with one another. Downward-facing inclined surfaces 1404 ofthe insert 1400 are facing toward complementary upward-facing inclinedsurfaces 1454 on the outer member 1450. As shown in FIG. 19B, when theannular flange or locking feature 1420 of the insert member ispositioned within the annular groove 1724 of the outer member, asufficient amount of force will dislodge screw head 1110 from the insertmember by shifting the annular wall portions 1411 of the insert member1400 outward, creating an opening large enough for the screw head 1110to escape. Consequently, the insert member 1400 and outer member 1450may be pre-assembled in this position, and the pedicle screw 1102 may beinserted and removed from the assembly relatively easily. The lockingfeature 1420 of the annular wall is allowed to shift outward because itis positioned in an annular expansion recess 1724 sized to allow forexpansion of the insert member.

As the outer member 1450 is pulled upward relative to the insert member1400 (so that the insert member 1400 shifts downward within the interiorspace of the outer member), the downward-facing inclined surfaces 1404of the insert retention tabs 1403 engage the complementary upward-facinginclined surfaces 1454 on the outer member retention tabs 1453, andbecause of their complementary inclined surfaces the tabs 1403 and 1453slide past one another. Flexible portions 1800 shift slightly inward toallow the retention tabs to slide past one another. Eventually, theinsert member retention tabs 1403 are shifted to a retention positionwherein the insert member retention tabs 1403 are located below theouter member tabs 1453, as shown in FIGS. 20A-B. Reaching this retentionposition may provide an audible click or other feedback as the insertmember tabs 1403 slide past the outer member tabs 1453, allowing theflexible arms 1800 to shift slightly outward to their originalpositions, snapping the insert member tabs 1403 into place below theouter member tabs 1453.

In this retention position, the insert member is permitted to shiftfurther downward into the outer member 1450, but resists shifting upwardbecause of flat abutment surfaces 1405 and 1455 on the trailing ends ofthe tabs. As shown in FIG. 20B, the tabs are positioned axially alongthe insert member and outer member so that when the tab abutmentsurfaces 1405 and 1455 meet, the annular camming locking feature 1420 ofthe lower portion of the insert member 1400 begins to engage a lockingfeature 1726 inside the outer member 1450, causing the annular wall 1411of the insert member 1400 to compress and shift slightly inward,applying a frictional force upon the screw head 1110. For instance, asdepicted, a tapered cam surface 1725 leads to the locking feature 1726,causing gradual compression of the lower annular wall 1411 of the insertmember 1400. In the position depicted in FIG. 20B, the compressive forceexerted against the lower portion 1860 of the insert member 1400 by thetapered camming surface 1725 is sufficient to prevent the screw head1110 from exiting the cavity formed by the annular wall 1411 of theinsert member 1400, but will not fully lock the coupling assemblyagainst pivoting with respect to the screw head 1110. The insertassembly 1400 resists backing out from this retention position due tothe interaction between the abutment surfaces 1455 of the outer membertabs 1453 and the abutment surfaces 1405 of the insert member tabs 1403.

Full locking of the screw head 1110, which prevents changes inangulation between the coupling assembly 1100 and screw 1102, isachieved again by pulling upward on the outer member 1450 (furthershifting the insert member 1400 downward relative to the interior of theouter member) so that the camming locking feature 1420 moves past thetapered cam surface 1725 of the outer member bore and into flush contactwith the inwardly-directed face of the annular locking feature 1726 atthe bottom of the bore, as depicted in FIG. 21B. In this full lockingposition, the insert member retention tabs 1403 are spaced below theouter member retention tabs 1453 so that the tabs no longer interact.Pairs of interacting tabs (for instance, first pair of tabs 1403 b, 1453b and second pair of tabs 1403 d, 1453 d depicted in FIG. 21A) arespaced far enough apart in a direction parallel to the rod axis (whichis generally orthogonal to the outer member axis) to allow lockingportions 1480 of a rod locking device such as cap 1408 to slide axiallyinto engagement with the flexible arms 1800 of the insert member todeflect the flexible arms 1800 inward and lock the rod in place, aspreviously described.

In another form, retention of the screw head prior to full locking maybe enhanced by configuring the coupling assembly and screw head so thatthe screw head is inserted into the cavity of the insert member in oneorientation and shifted or rotated to a second orientation to resistwithdrawal of the screw head from the cavity. For instance, as depictedin FIGS. 22-25, a screw 2102 is provided having a head portion 2110 witha height (“h”), a first head width (“x”) and a second head width (“y”),where the first head width is larger than the second head width. In thismanner, the head is sized and shaped so that it may enter and exit thecavity of the insert member more easily in one orientation than inanother orientation. The form of screw head depicted in FIGS. 22A-Cforms essentially a truncated sphere, with a partially spherical profilewhen viewed from one transverse direction (FIG. 22B) and a wedge-shapedprofile when viewed from a second transverse direction (FIG. 22C). Thiswedge shape facilitates alignment and insertion of the screw head withthe opening in the insert member for snap-locking therein.

The screw head of FIGS. 22A-C is received in a complementarilyconfigured insert member 2400, depicted in FIGS. 23A and 23B. As withother exemplary insert members described herein, the insert memberincludes expansion gaps 2810 for allowing the annular wall portions 2411of the insert member to flex for receiving a screw head therebetween ina snap-lock manner. As with other embodiments, the expansion gaps 2810also allow the annular wall portions 2411 to be compressed or compacted,applying a frictional force onto the screw head to lock it in place.Major expansion gaps 2810 a allow for relatively large amounts offlexion due to their length, while minor expansion gaps 2810 b permitrelatively less flexion. As shown in FIG. 23B, an opening 2860 in thelower portion of the insert member is configured to receive a screwhead. The opening 2860 has a first width (“a”) that is larger than asecond width (“b”). The first, longer width lies transverse to the majorexpansion gaps 2810 a, so that the opening widens in the direction ofthe greater opening width (“a”).

In use, the screw of FIGS. 22A-C may be inserted relatively easily intothe insert member of FIGS. 23A-B when the first, larger, width of thescrew head (“x”) is aligned with the first, larger width (“a”) of theopening 2860 in the lower end of the insert member 2400, but resistsinsertion from other orientations, such as when the first, larger width(“x”) of the screw head is aligned with the second, narrower width (“b”)of the opening in the insert member. Insertion and retention of thescrew head into the insert member is demonstrated in FIGS. 24A-C, whichdepict a perspective view of the screw and a cut-away perspective viewof the insert member 2400. Similar to other embodiments describedherein, as the screw head is inserted into the cavity 2820 of the insertmember 2400, as shown in FIG. 24A, major expansion gaps 2810 a allow theinsert member 2400 to flex, expanding the volume of the insert cavity2820. Once the partially spherical surfaces 2127 of the head 2110 enterinto the cavity, the flexible walls of the insert member flex backtoward their original positions, closing around the screw head 2110 in asnap-lock arrangement. Although the insert member 2400 is at that pointcoupled to the screw head 2110, the insert member may still be removedwith relative ease. For instance, the coupling assembly and screw headmay be configured so that the coupling assembly may be removed by hand.In order to more securely hold the screw head, the insert member 2400 isrotated a predetermined amount (such as the approximately 90 degreerotation depicted) with respect to the screw 2102, so that the greaterwidth of the insert member opening and the greater width of the screwhead are out of phase, as shown in FIGS. 24 c and 25B. The greater screwhead width (x) is then aligned with the major expansion gaps 2810 a.

Whereas the screw head 2110 contacts the annular wall portions of theinsert member at points 2421 a and 2421 b in the insertion position(FIG. 25A), allowing the screw head to exit the insert member byexpanding expansion gaps 2810 a, in the retention position (FIG. 25B)the screw head 2110 does not contact wall portions 2421 a and 2421 b,and thus it is more difficult for forces applied to the screw or insertmember to cause expansion of major expansion gaps 2810 a. Thus, when theinsert member is rotated to the screw retention position shown in FIGS.24C and 25B, a greater amount of force must be applied to remove thescrew head from the insert member cavity than when in the insertionposition of FIGS. 24B and 25A. Advantageously, the screw head and insertmember opening may be configured so that rotation of the insert memberto this screw retention position ensures that the screw head will notescape the insert member cavity while the insert member is manipulatedand placed under loads to engage and capture a spinal rod prior tolocking of the assembly. Final locking of the screw relative to theinsert member may be accomplished by axially shifting an outer memberover the insert member 2400 in a manner similar to that described inconnection with other embodiments herein.

Exemplary Embodiments of FIGS. 26-41 with Offset Anchor Heads forIncreased Angulation

Certain vertebrae of the spine are smaller than others, presentingcertain difficulties during the implantation, positioning, and securingof devices intended to fix a spinal rod or other member to the spine.For instance, the cervical vertebrae (located in the neck) are muchsmaller than vertebrae in other portions of the spine, such as in thelumbar region. Therefore, pedicle screws or hooks mounted to thecervical spine must be positioned much closer to one another.Additionally, since the cervical region is curved, accessing thevertebrae from a posterior approach is more difficult than in otherregions of the spine. Although the following embodiments are describedas being particularly useful for implantation in the cervical spine,they may also be used in connection with vertebrae from other portionsof the spinal column, especially where wider angulation of the anchormember is beneficial.

An embodiment of a novel pedicle screw assembly designed for use when itis desired for the anchor member to be able to be pivoted to an extremeangle relative to the axis of the coupling device is shown in FIGS. 26and 27. FIG. 26 shows the assembled device 3010 secured to a spinal rod3025, while FIG. 27 shows an exploded view of the device. As with otherembodiments, the anchor member need not be a pedicle screw, and couldinstead be a hook, clamp, or other mounting device. The illustratedscrew assembly 3010 includes an anchor member 3020 in the form of apedicle screw with external threads 3021 formed along the shank 3020; anouter member or yoke 3030; an insert member or core member 3050; and arod locking member in the form of a cap member 3070. Although theconfiguration of the assembly as illustrated is generally cylindrical,other shapes and configurations are also possible. In addition, theexterior of the illustrated assembly, and specifically the yoke member3030 has exterior flat faces 3044 that are aligned with the upperchannel slot 3035 in which the rod 3025 is received, reducing theprofile along the length of the rod. These flat faces 3044 thereforeallow more assemblies to be connected along a given length of the spinalrod than would otherwise be possible, and in addition reduce the massand material required for manufacture of the coupling assembly.

As with other embodiments, the screw assembly 3010 secures a spinal rod3025 by urging the arms of the insert or inner core member 3050 inwardlytoward each other and against the surface of the rod 3025, fixing therod in place with respect to the anchor member 3020. The position of theanchor member 3020 is fixed by shifting the outer member 3030 over theinsert member 3050, compressing the lower portion of the insert memberagainst the head 3025 of the anchor located within a cavity of theinsert member 3050. In the illustrated embodiment, the outer member oryoke 3030 is generally cylindrical in shape, albeit with the previouslydescribed diametrically opposite flat portions 3044 along its outersurface, with laterally extending shoulder portions 3031 on either sideof the channel 3035 through which the rod 3025 passes. The shelf 3032underneath each shoulder portion may be used to grip the yoke 3030 inorder to shift the yoke with respect to the inner core member 3050. Forinstance, a tool may be used to grip one or more portions of the shelves3032, with an upward force from the tool shifting the yoke 3030 upwardwith respect to the inner core member 3050. In the illustratedembodiment, a central tapered recess 3033 is located within the shoulderportion 3031 to facilitate centering of a gripping tool along the shelf3032. Sloped surfaces forming the sides of the recess 3033 naturallylead a gripping tool to the peak at the center of the recess 3033.

The cap member 3070 associated with the embodiment shown in FIGS. 26 and27 is provided with a central opening 3075 providing a surface which maybe grasped by an instrument or tool for inserting or removing the cap.The opening 3075 allows the cap 3070 to be manipulated without graspingat the outer edges 3076 of the cap, allowing a centralized force to pushthe cap into place and to pull the cap out from the yoke 3030. Forinstance, a driving member may be equipped with projections thatsnap-lock into the opening 3075 in the top of the cap member 3070 tohold the cap member in place during insertion, or to grip the cap forremoval. Since wedging the legs 3071 of the cap member between the outermember 3030 and the arms 3051 of the insert core member 3050 locks thespinal rod in place, the cap need not contact the spinal rod even whenfully locked, and in fact may be designed with a clearance on theunderside of the cap in order to avoid contact with the rod.

FIG. 27 is an exploded view of the pedicle screw system of FIG. 26,showing the pedicle screw assembly 3010 in a disassembled state. In thisview, details of the individual components of the assembly may be moreclearly viewed. For instance, the entire cap member 3070 is shown and itincludes a generally cylindrical or disk-like body portion 3077 havinglegs 3071 extending downward from the top portion. In the illustratedembodiment, the lateral edges of the cap top portion contain lips orridges 3072 to help secure the cap within the yoke 3030 upon fullinsertion. The lips 3072 shown include a sloped bottom surface to bemore easily inserted downward. A flat upper surface of the lip 3072prevents the cap from backing out from the yoke once inserted byabutting a ridge 3036 on the interior of the outer member 3030.Similarly, the cap legs 3071 as depicted each contain a laterallyextending foot portion 3073 for snap locking into the yoke 3033 afterpassing the outer member interior ridge 3036. The lower surface 3074 ofthe foot portion 3073 allows the foot portion to be easily inserted intothe yoke, while a flat upper surface of the foot prevents retrogrademotion of the cap past ridge 3036.

The fixation member depicted in FIG. 27 is a screw member having agenerally spherical head 3025 and a shank 3022 with threads 3021 alongthe length of the shank 3022. In the illustrated embodiment, the head ofthe screw 3020 is offset from the shank so that the center 3025 a of thehead portion 3025 offset from the central axis 3026 of the shank 3022. Aneck portion 3024 links the head portion 3025 to the shank. This offsethead configuration allows the shank to be pivoted to a more pronouncedangle in one direction than would be possible if the head portion werealigned along the axis of the shank, as explained further below inconnection with FIG. 30 d. Alternatively, if increased angulation is notnecessary a normal screw may be employed, with the head disposeddirectly above the shank so that the center of the head is in alignmentwith the central longitudinal axis of the shank. Furthermore, it iscontemplated that other forms of anchor members for securing theassembly to the vertebrae may be used, such as hooks or clamps.Likewise, use of the offset head anchor member is not limited to thetypes of coupling members disclosed herein, and may be used inconjunction with other coupling devices known in the art.

FIGS. 28A-B show the screw fixation member 3020 in greater detail. Thistype of anchor may be used with any of the coupling devices describedherein, as well as in other types of coupling devices. As previouslydescribed, helical threads 3021 winding around the shank portion 3022secure the assembly to bone. The central longitudinal axis of the shankportion 3022 is shown by dashed line 3026. The generally spherical headportion 3025 of the fixation member has a center 3025 a that is notaligned with the shank axis 3026. A line that passes through the center3025 a of the head 3025 and through the center of the upper drive recessor socket 3023 is the central axis of the screw head portion 3025 and isshown as dashed line 3027. This screw head axis 3027 does not coincidewith the shank longitudinal axis 3026. This offset head allows a normalrange of pivoting for an associated coupling member when the screw 3020is mounted at an angle into a vertebra, as explained below in connectionwith FIG. 35. This is particularly advantageous in the cervical spine,which is curved and relatively small so that it is not always possibleto implant an anchor member perpendicular to a vertebra.

A cutaway portion 3029 may be provided towards the tip of the screw tofacilitate penetration of bone. The screw may also be provided with anopening to a central cannula running axially through the screw shank3022. A guide wire may be passed through the cannula in order to directthe screw along a predetermined path, making the screw well suited forminimally invasive surgery.

As shown in FIG. 28B, the drive recess 3023 is located in the headportion 3025 in order to receive an insertion tool for driving the screwinto bone. Recess 3023 may have a polygonal or irregular shape so thatrotation of an insertion tool within the recess 3023 causes rotation ofthe screw 3020. Since the head portion is offset from the shank axis,however, rotating a tool within the recess 3023 will cause the screwshank 3022 to orbitally rotate about the head portion 3025 rather thanto simply bore into the bone, complicating the anchoring process unlessa specialized tool is employed, as described below.

The exemplary coupling assembly 3010 is shown mounted to the pedicle3001 of a vertebra 3002 via the screw 3020 in FIG. 29. The illustratedscrew 3020 is the offset angle screw as shown in FIGS. 28A-B.

The insert member 3050 of the device shown in FIG. 27 is shown in moredetail in FIGS. 30A-B. As with other embodiments described herein, theinsert member or core member 3050 is provided to receive the rod and thefixation member. The exemplary core member 3050 includes a base portion3055 having a generally disk shape. Arms 3051 extend upward from thebase portion 3055 forming a channel 3065 between the arms in which thespinal rod or similar member is received. The rod may be gripped bycontact features on the interior of the arms, such as one or moreprojections. In the illustrated core member 3050, a groove 3052 runsalong the length of each arm 3051 in the direction of the channel. Whenthe rod is received in the channel 3051, the most lateral surfaces ofthe rod will rest in these grooves 3052, providing a snap fit to lightlyretain the rod within the channel 3065 without use of a locking membersuch as a cap member (3070, FIGS. 26-27).

Extending from the underside of the base portion 3055 of the core memberare four finger-like projections 3062 for gripping the head of theanchor member. The projections 3062 are sized and configured to form apocket in which the anchor head may be retained. The finger-likeprojections 3062 as depicted are equally spaced by four compression gaps3061, but other configurations are possible with different numbers offinger-like projections and compression gaps. In the illustratedembodiment, the compression gaps 3061 are equally spaced around thecircumference of the core member 3050 and are of equal length, extendingup to the base portion 3055. The gaps 3061 allow the finger-likeprojections 3062 to flex outward, expanding the lower portion of thecore member 3050 to receive the head of the fixation member in asnap-lock manner. The gaps 3061 also allow the finger-like projections3062 to be forced inward to compress around the head of the anchormember, locking the anchor member in place at a desired angle with africtional force.

The finger-like projections 3062 of the illustrated insert memberinclude a step formation forming a tapered lower portion for the coremember 3050. In the illustrated embodiment, the base portion 3055 formsa first step, while a second step 3056 located below is positionedradially inward from the base portion 3055. The third step 3057 ispositioned radially inward from the second step 3056. Although a smooth,continuous tapered surface could be employed in the core member 3050,the steps 3055, 3056, and 3057 allow the core member to be shifted intothree discrete positions within the yoke 3030 to cause the finger-likeprojections 3062 to apply a predetermined amount of locking force ontothe anchor head captured therein. The surgeon manipulating the pediclescrew assembly also receives tactile feedback while shifting the coremember 3050 within the yoke 3030, as transitioning from one step toanother involves a sudden increase in the frictional force between thecore member 3050 and the yoke 3030. In order to facilitate insertion ofthe core member 3050 into the yoke or outer member, steps 3055, 3056,and 3057 are each provided with a beveled edge 3085, 3086, and 3087,respectively, that will interact with the yoke to force the finger-likeprojections progressively more inward as the core member 3050 isinserted further into the yoke.

The above-identified structures of the insert member are shown frombelow in FIG. 30B, where it can be seen that the finger-like projections3062 form a generally spherical cavity 3063. The cavity pivotablyreceives the generally spherical head portion 3025 of the anchor member3020, as shown in front cross-section (FIG. 30C) and side cross-section(FIG. 30D), which both illustrate a pedicle screw 3020 with an offsethead 3025 received in the core member 3050. As best seen from FIG. 30 d,the offset configuration of the anchor head portion reduces interferencebetween the anchor shank 3022 or other attachment portion and the coreinset member 3050. The shank is positioned toward one side of the head3025 (toward the left in FIG. 30D), so that as the anchor is pivotedforward (toward the right in FIG. 30D) movement is not limited until theneck portion 3024 of the anchor abuts the lower edge 3064 of the insertmember. Due to the offset nature of the head portion, one side of theneck 3024 is located much closer to the center of the head than it wouldbe if the head portion were aligned with the axis of the shank. Thisallows a significantly greater ability of the shank 3022 to pivot in onedirection (to the right in FIG. 30 d). For instance, the screw may beconfigured to allow the shank 3022 to pivot 60 degrees or more away froma central axis of the coupling device. The screw may even be configuredto achieve a 90 degree angle if desired, so that the shank 3022 isdirected to the side of the coupling device.

As previously described with respect to other embodiments, retentiontabs 3077 (FIG. 30A) are located on the arms of the core member 3050 tointeract with complementary retention tabs 3047 located on the yoke 3030(FIGS. 31A, 32A; described below). As the core member 3050 is insertedinto the axial bore 3035 of the yoke 3030 (FIGS. 27, 31A-B), retentiontabs 3077 on the core will pass retention tabs 3077 on the yoke due todownward sloped surfaces on the core retention tabs 3077 and upwardsloped surfaces on the yoke retention tabs 3047, allowing for one-wayshifting of the core member 3050 into the space within the yoke.

The yoke member 3030, shown in FIGS. 26-27 is shown in greater detail inFIGS. 31A and 31B and includes upright portions 3040 which form an openchannel 3041 in which the rod may be received. In the illustratedembodiment, a large portion of the channel is wider than necessary forthe rod to be received between the uprights 3040. A cylindrical recessor seat 3037 is located at the bottom of the channel configured toconform to the surface of the spinal rod. A generally cylindrical axialbore 3035 is formed within the center of the yoke 3030. The interiorsurface of the axial is bore is stepped to complement the finger-likeprojections 3062 of the insert member 3050 (FIGS. 30A-D). As shown inFIG. 31B, interior stepped locking features 3085, 3059, and 3060 arepositioned concentrically to sequentially compress inward thefinger-like projections of the core member (FIGS. 30A-D) as the core isshifted further downward through the open space or bore 3035 in the yoke3030.

The upright portions 3040 of the yoke 3030 contain laterally extendingshoulder portions 3031 which may be grasped to manipulate the outermember. The base portion 3042 of the yoke 3030 is generally cylindricalin shape, but flat surfaces 3044 are located adjacent to the rod channel3037 in order to reduce the profile of the assembly along the length ofthe rod. This allows placement of several coupling assemblies adjacentone another along a relatively short length of rod, which isadvantageous in areas such as the cervical spine, where the vertebraeare small in size.

As noted above, the yoke 3030 contains retention tabs 3047 located alongthe rod channel 3041 in order to interact with retention tabs 3077 onthe core member. As the core member 3050 (FIGS. 27, 31A-D) is insertedinto the axial bore 3035 of the yoke 3030, retention tabs 3077 on thecore will pass retention tabs 3077 on the yoke due to downward slopedsurfaces on the core retention tabs 3077 and upward sloped surfaces onthe yoke retention tabs 3047, allowing for one-way shifting of the coremember 3050 into the space within the yoke. The shape of thecomplementary retention tabs 3047, 3077, having a sloped or rampedsurface on one side and an abutment surface on the other side, allowsthe core member 3050 to be linearly shifted into the yoke 3030 in adownward direction, but prevents retrograde motion once the retentiontabs 3047 and 3077 have passed one another, so that the core does notback out of the yoke. If desired, additional retention features could beplaced to provide for additional retention points, allowing for linearratcheted movement of the core member into the yoke.

FIGS. 32A-D illustrate locking of the full coupling assembly. In FIGS.32A and 32C, the core member 3050 is partially inserted into the yoke3030, and yoke retention tabs 3047 interact with core member retentiontabs 3077 to prevent upward movement of the core 3050 out of the spacewithin the yoke 3030. Downward movement of the core 3050 relative to theyoke 3030 is still allowed. The rod 3025 is shown snapped into the coremember 3050, received between the arms 3051 of the core member, with thelateral surfaces of the rod 3025 resting in the retention grooves 3052of the arms. As shown in cross-section (FIG. 32C), the cap issnap-locked into the assembly, with the feet 3073 of the cap legs 3071retained by a lip 3078 of the yoke 3080. However, the cap legs 3071 arenot yet wedged between the arms 3051 of the core 3050 and the uprightportions 3040 of the yoke 3030. The anchor member 3020, although coupledto the assembly, is not locked into place, since the locking features onthe inside surface of the yoke member hollow space 3030 have not yetbeen forced into contact with their respective step portions on thefinger-like projections of the core member 3050. For instance, the mostradially-inward step portion, 3057, is not aligned with the mostradially-inward locking feature 3060. Instead, step portion 3057 isaligned with a wider locking feature, 3059. Nevertheless, alignment ofstep portion 3057 with wider locking feature 3059 may be configured tocause some compression of the lower portion of the core member 3050,retaining the anchor member in place and possibly even applying somefrictional force between the core member 3050 and the anchor head 3025to reduce pivoting of the anchor member 3020.

Full locking of the assembly is shown in FIGS. 32B and 32D. In thisposition, the cap 3070 is fully inserted into the assembly, and legs3071 of the cap are wedged between the upright arms 3051 of the coremember and the upright portions 3040 of the yoke 3030. As seen incross-section (FIG. 32D), an upper ridge or lip 3072 on the cap 3070 maysnap-lock into the yoke 3030 as it is shifted past a lip 3078 of theyoke, further securing the cap 3070 to the assembly. Furthermore, themost radially-inward step portion, 3057, is now aligned with the mostradially-inward locking feature 3060. Furthermore, step 3056 is alignedwith corresponding locking feature 3058. This configuration providesmaximum compression force from the yoke 3030 onto the finger-likeprojections 3062 of the core, locking the anchor head 3025 at a setposition within the core and preventing further pivoting of the anchormember 3020.

Another embodiment of a novel pedicle screw assembly designed for use inthe cervical region of the spine is shown in FIGS. 33-37. In manyrespects this design is similar to that shown in FIGS. 26-32D, but ismore streamlined. The pedicle system in FIGS. 33-37, as those describedabove, includes an outer member or yoke 4030, an insert member or coremember 4050 having upright arms 4051 for receiving a spinal rod 4025, acap member 4070 or other rod locking member, and an anchor member 4020.The illustrated anchor member 4020 is an offset pedicle screw, asdescribed above, which allows the coupling assembly 4010 to be pivotedat extreme angles with respect to the anchor member 4020 even when theanchor member 4020 is initially inserted at an angle.

FIG. 34 provides an exploded view of the pedicle screw system of FIG.33, showing this embodiment of the pedicle screw assembly 4010 in adisassembled state. In this view, details of the individual componentsof the assembly may be more clearly viewed. Cap member 4070 includes agenerally cylindrical or disk-like top portion 4077 having legs 4071extending downward from the top portion. The cap is shown in more detailin FIGS. 37A-C. Unlike the previously described embodiment (FIG. 27),the cap 4070 does not have a lip near the top portion, reducing theforce necessary for full insertion and removal of the cap. The insertmember or core member 4050 of the embodiment shown in FIGS. 33-35contains finger-like projections 4062 with a two-step structure, withstep portions 4057 and 4056 for interacting with the interior of theyoke 4030.

As shown in FIG. 35, the offset anchor member 4020 may be mounted tobone 4001 at an angle and still permit a normal range of motionequivalent to that of a straight anchor member mounted substantiallyperpendicular to the bone. Since pivoting of the coupling device 4010with respect to the anchor member head 4025 is limited by abutment ofthe device 4010 against the anchor shank 4022, offsetting the shank 4020from the center of the head portion 4025 increases pivotability in onedirection while decreasing pivotability in the opposite direction. Inessence, this shifts the axis about which the device 4010 pivots whencoupled to the anchor head. The anchor member 4020 and its head portion4025 and shank portion 4022 are configured so that when the anchor ismounted at a specific angle relative to a vertebra and/or a couplingassembly, the head still allows pivoting of the coupling assembly 4010of Ø in any direction with respect to an axis or plane normal to thesurface of the bone 4001 in which the anchor is mounted. The couplingassembly 4010 depicted in FIG. 35 would not be allowed to pivot forwardto the extent shown if the anchor head 4025 were mounted along the axisof the anchor's shank 4021. The loss of pivotability in one direction isnot detrimental, since the anchor 4020 may be rotated 360° within thegenerally spherical cavity of the insert member 4050 in order to orientthe anchor 4020 so that it points in a desired direction. Thepositioning of the head portion 4025 with respect to the shank 4022 maybe altered if desired, and different configurations will offer differentmaximum amounts of pivotability.

The core member 4050 of the device in FIGS. 33-35 is shown in moredetail in FIG. 36. Similar to insert core members described above, thecore includes a channel 4065 for receiving a rod between two uprightarms 4051. The lower portion of the core includes a two-stepconfiguration with a wider portion 4056 and a narrower portion 4057configured to be disposed against complementary locking surfaces on theinterior of the outer member or yoke 4030. In order to lock the anchormember 4020 in position, the step portions 4056 and 4057 are shiftedinto alignment with locking features 4059 and 4060, respectively.Compression slits 4061 a and 4061 b allow the wall portions 4062 to bedeflected inward against the head of an anchor member receivedtherebetween and are configured to have different heights to takeadvantage of the increased height of the sides of the core member due tothe upright arms 4051.

The cap member 4070 of the device in FIGS. 33-35 is shown in furtherdetail in FIGS. 37A, 37B, and 37C. The cap member 4070 includes arelatively thin body portion 4077 and relatively thick and rigid legportions 4071. The leg portions 4071 are thicker near the cap bodyportion 4077 in order to provide greater locking force when the cap isfully inserted than when the cap is partially inserted between the coremember 4050 and outer yoke member 4030. The underside 4079 of the capmember has a partially cylindrical recess that can be either configuredto sit flush with the exterior of the spinal rod or avoid contact withthe spinal rod, depending on the length of the cap legs 4071 and thethickness of the cap body 4077. A central aperture 4075 provides a pointof attachment for a cap insertion instrument, and also reduces the massof the cap. Outwardly-directed feet 4073 on the leg portions allow thecap to be provisionally held within the outer body portion 4030 aspreviously described in connection with other embodiments.

Yet another embodiment of a pedicle screw system appropriate for use inthe cervical spine is shown in FIGS. 38-41. As can bee seen, thisembodiment has a thicker cap 5070, and an extremely slim profile whenviewed from the side. The illustrated anchor member is straight,although an offset-angle anchor member may also be used.

The pedicle system contains an outer member or yoke 5030, an insertmember or core member 5050 having upright arms 5051 for receiving aspinal rod, a cap member 5070 or other rod locking member, and an anchormember 5020. The illustrated anchor member 5020 is a traditional pediclescrew, although alternatively an offset-head pedicles screw as discussedabove may be used to allow the coupling assembly 5010 to be pivoted atextreme angles with respect to the anchor member even when the anchormember is initially inserted at an angle. FIG. 38 shows the anchor 5020,the yoke 5030, and the core insert 5050 assembled, with the cap member5070 removed. The above structures are shown in cross-section in FIG.39, which shows that the core insert may have a two-stepped exteriorconfiguration to provide a partial lock and final lock when positionedagainst corresponding surfaces on the interior surface of the yokemember 5030.

Insertion of the cap member 5070 is shown in FIG. 40. The legs 5071 ofthe cap member 5070 are designed to be wedged between the upright arms5051 of the insert member 5050 and the interior surface of the outeryoke member 5030. The generally cylindrical body 5077 of the cap member5070 has a substantial thickness to provide additional rigidity to thecoupling assembly when fully locked.

The assembly of FIGS. 38-40 is shown from the exterior in perspective inFIG. 41. The shoulders of the yoke contain features to be engaged by aninstrument for locking or manipulating the assembly. The outer surfaceof the outer yoke 5030 is curved toward the bottom to reduce the overallprofile of the assembly.

FIG. 34 provides an exploded view of the pedicle screw system of FIG.33, showing this embodiment of the pedicle screw assembly 4010 in adisassembled state. In this view, details of the individual componentsof the assembly may be more clearly viewed. Cap member 4070 includes agenerally Cylindrical or disk-like top portion 4077 having legs 4071extending downward from the top portion. The cap is shown in more detailin FIGS. 37A-C. Unlike the previously described embodiment (FIG. 27),the cap 4070 does not have a lip near the top portion, reducing theforce necessary for full insertion and removal of the cap. The insertmember or core member 4050 of the embodiment shown in FIGS. 33-35contains finger-like projections 4062 with a two-step structure, withstep portions 4057 and 4056 for interacting with the interior of theyoke 4030. The core member 4050 is shown in more detail in FIG. 36. Inorder to lock the anchor member 4020 in position, the step portions 4056and 4057 are shifted into alignment with locking features 4059 and 4060,respectively.

As shown in FIG. 35, the offset angle anchor member 4020 may be mountedto bone 4001 at an angle and still permit a normal range of motionequivalent to that of a straight anchor member mounted substantiallyperpendicular to the bone. The anchor member 4020 and its head portion4025 are designed so that when the anchor is mounted at a specificangle, the head still allows pivoting of the coupling assembly 4010 of Øin any direction with respect to an axis normal to the surface of thebone 4001 in which the anchor is mounted. The coupling assembly 4010depicted in FIG. 35 would not be allowed to pivot forward to the extentshown if the anchor head 4025 were mounted along the axis of theanchor's shank 4021.

Exemplary Screw Inserter Tools for Use with Offset Angle Screws

FIGS. 42-43 depict a screw inserter and driver for use with an offsetangle screw as described above. The illustrated inserter 6010 has ashaft 6050 and an interface drive portion or projection 6070 forinterfacing with the drive socket 6023 of the offset head portion 6025of a pedicle screw 6020 (or, for instance, the drive socket 3023 of theoffset head portion 3025 of a pedicle screw 3020 of FIG. 28B). The driveprojection 6070 is not aligned with the axis of the shaft 6050. As shownin FIG. 43, since the drive projection 6070 is not aligned with thecentral axis of the shaft portion 6050 of the tool, it may be used tointerface with the head 6025 of the offset pedicle screw 6020 so thatthe threaded shank 6021 of the screw is aligned along the shaft axis ofthe inserter tool. In other words, since both the tool drive projection6070 and the screw head 6025 are out of alignment and offset from theirassociated axial portions by an equal and offset amount, aligning thetool's drive projection 6070 with the recess 6023 in the screw head 6025aligns the tool shaft 6050 with the screw shank 6021 just as a normal,straight screw shank is aligned with the shaft of a normal insertiontool. Therefore, rotation of the tool shaft 6050 rotates the driveprojection 6070 received in the screw head socket 6023 and the offsetscrew head 6025 orbitally around the screw shank 6021 so that the screwshank 6021 is rotated about its axis in order to threadingly drive theshank into bone. In order to facilitate connection between the insertertool 6010 and the screw head 6025 with such an offset configuration, thetool's drive projection 6070 and the recess 6023 in the screw head 6025may be configured to only fit together in one orientation.

The screw inserter 6010 may also include a core lock member 6060configured much like a spinal rod and positioned to extend transverselyto the tool shaft 6050. The core lock member 6060 imitates a spinal rodand may be used to capture a core member or insert of a pedicle screwsystem, such as the type described above, to insert a screw into bonewhen the screw is already coupled to the core member. The core lockmember 6060 is disposed within the rod channel of the core member (e.g.3065 of FIG. 30A) and the drive protrusion 6070 is disposed in the drivesocket 6023 of the offset head portion 6025 held within the core member3065 so that both the core member 3065 and the screw 6020 are rotated byrotation of the tool. Due to the offset nature of the screw head 6025,the core member 3065 will rotate orbitally around the axis of the screwshank and the axis of the tool shaft 6050.

Other inserter tools and variations of the described embodiment may alsobe used. The interface portion 6070 may, for instance, be aligned alongthe tool axis 6050, or the core lock member 6060 may be removed.Traditional inserters may also be used, but are not preferred.

Exemplary Transverse Connection Devices

When a series of pedicles screws are used to mount two or more rods to apatient's spine, a transverse connector or cross connector may be usedto link two spinal rods. An exemplary transverse connector is shown inFIGS. 44A-47. The transverse connector 7010 includes a first arm 7020having a first head 7030 for receiving a first spinal rod, and a secondarm 7040 having a second head 7050 for receiving a second spinal rod.The first head 7030 has a cam actuator member 7035 that when rotatedshifts a clamp member or jaw member 7037 upward to clamp a spinal rod inplace within the rod seat 7032 in the first head. Likewise, the secondhead 7050 has a cam actuator member 7055 that shifts a clamp member orjaw 7057 upward to clamp a spinal rod in place within the rod seat 7052in the second head. Advantageously, the cam members are each generallycylindrical with an axis therethrough, and have non-threaded contouredsurfaces that cause them to shift axially in the head portions whenrotated so that the clamp members 7057 and 7037 move from fully open tofully clamped when the cam members 7055 and 7035 are rotated less than360°. However, alternatively other actuator members may be used in placeof the illustrated cam members 7035 and 7055. For instance, threadedscrews may be used to shift clamp members 7057 and 7037, with thethreading on the screws configured to match complementary threading onthe interior of the head portions 7030 and 7050.

The two arms 7020 and 7040 of the transverse connector 7010 arepositioned relative to one another using an adjustment device. Theillustrated adjustment device 7018 has a head portion 7015 that may beturned to lock and unlock the arms. The head portion 7015 is connectedto a threaded portion 7016 that is threaded into a threaded orifice 7019in the second arm 7040. Rotating the head portion 7015 and associatedthreaded portion 7017 clamps the arms 7020 and 7040 together, preventingrelative movement of the two arms. A washer member 7017 is provided tofacilitate clamping of the arms and to prevent accidental unlocking.When the adjustment device 7018 is unlocked, the arms may be shiftedlinearly to increase or decrease the width of the device. During linearadjustment, the adjustment device 7018 moves back and forth through aslot 7025 in the first arm 7020. FIG. 45 shows the transverse connectorin a compact configuration, where the arms 7020 and 7040 almostcompletely overlap. FIG. 46, in contrast, shows an extendedconfiguration wherein there is minimal overlap between the two arms. Inaddition to linear adjustment, the arms 7020 and 7040 may be pivotedwith respect to one another so that the heads 7030 and 7050 may capturenon-parallel portions of spinal rods. The arms 7020 and 7040 pivot aboutthe adjustment device 7018 when it is in the unlocked configuration.Upon turning of the adjustment device 7018, the arms are clampedtogether, preventing both sliding and pivoting of the arms. Thus, thesingle adjustment device is sufficient to lock the transverse connectoragainst further linear and angular adjustment. Although shown as athreaded member, the adjustment device 7018 may incorporate a camactuator similar to those in the head portions or other such devices toclamp the arms of the connector together.

In the illustrated embodiment, the arms 7020 and 7040 are relativelyflat in order to substantially reduce the profile of the transverseconnector. In addition, both arms 7020 and 7040 are arched, in order toprovide clearance underneath the cross-connector. This allows thetransverse connector to connect spinal rods across bony protrusions orother tissue without interfering with such tissues or requiring theirremoval.

Exemplary Reducer/Inserter Instrument

A reducer/inserter tool may also be provided for reducing a spinal rodinto a coupling device and inserting a cap member to lock the positionof the rod. One exemplary reducer/inserter tool is shown in FIGS. 48-52.One advantage of the reducer inserter tool is the ability to quickly andefficiently provide rod reduction and cap locking in one tool. Anotheradvantage of the present reducer inserter tool is the simplicity indesign and operation. The reducer inserter tool operates throughmanipulation of a lever 10321 configured to actuate a reducing mechanismand a handle 10413 to actuate a cap driving mechanism. The simpleoperation simplifies manufacturing, reduces training, and improvesreliability of the reducer inserter tool.

Finally, another advantage present in the reducer inserter tool is thelow weight of the reducer inserter tool. The reducer inserter tool maybe made from materials such as titanium, Nitinol, stainless steelalloys, or combinations thereof, and the amounts of those materials maybe minimized to reduce weight of the tool. The manufacture and materialcomposition of the tool is not readily apparent to the user butfunctions to reduce surgeon fatigue after repeated operations of thetool and to reduce the risk of injury to the patient. The risk of injuryto the patient is minimized because the light weight of the toolprevents excessive momentum and force from building as the tool movesfrom one location on the spine to another. Should the tool impact thespine the reduced weight of the tool reduces the corresponding impact onthe spine and attached spinal cord.

The reducer/inserter tool 10001 shown in FIGS. 48-54 secures a spinalrod in a coupling device of the type described in connection with FIGS.1-41. The tool 10001 reduces the spinal rod into the device and theninserts a cap or other lock member into the device to lock the rod inplace. In one form, the assembly manipulated by the reducer/insertertool 10001 has an insert member that couples to a screw and a rod, anouter member that shifts in a first direction over the insert to lockthe screw in place, and a cap member that is inserted between the insertand outer members in a second direction opposite the first direction tolock the position of the rod. The reducer inserter tool containsstructures to shift the outer member and cap member relative to theinsert member to secure the rod and lock the screw in the assembly toprevent pivoting therebetween.

The reducer/inserter tool includes an outer shaft portion 10101 that hasa distal head portion 10201 as shown in FIG. 48 for grasping the outermember of the coupling device. As shown in FIG. 48B, the outer shafthead portion has an access port 10205 that receives the coupling devicefrom a side of the tool. The head portion 10201 is open at the end toallow the anchor member of the coupling device to pass therethrough whenthe coupling device is received in the head portion 10201. The couplingdevice is received through a side access port 10205 so that the enlargedshoulder portion of the coupling device outer member (or a similarstructure designed to be grasped by a tool) may slide above projections10203 on the interior of the outer member. The projections 10203 preventthe coupling device from being pushed out through the opening in thebottom of the head portion 10201 when downward force is applied by thetool to reduce the spinal rod into the coupling device.

The head portion is shown in greater detail in FIGS. 51A and 51B.Projections 10203 on the interior of the head portion 10201 allow thehead portion 10201 to grasp the coupling device from the underside of ashoulder portion or other surface feature (for example, shoulder recess3033 in FIG. 26). When the coupling device is under compressive loadingduring the reduction of the rod into the insert member, then theshoulder recess 3033 in the underside of the shoulder of the screwassembly will self-center the projection 10203.

As shown in FIGS. 48A-B, the outer shaft portion 10101 is coupled to ahandle 10131 to allow the surgeon to grasp the tool 10001. Asillustrated in FIGS. 48A-B, the handle 10131 is connected to theexterior of the outer shaft 10101 by pins 10133, screws 10135, and aplate 10137, although other methods may alternatively be used.

Rod reduction is accomplished by manipulation of the reducing lever10321. As shown in FIG. 49, the hollow reducing shaft 10341 is disposedconcentrically within the outer shaft 10101 and connected to thereducing lever 10321 via a linkage. The linkage connects the lever 10321to the reducing shaft 10341 through elongate openings in the outer shaft10101 so that pivoting of the lever 10321 causes axial shifting of thereducing shaft 10341 within the outer shaft 10101. The tip of thereducing shaft is configured to interface with the exterior of a spinalrod, so that linear shifting of the reducer shaft 10341 is capable ofdriving the spinal rod into the coupling member with significant force.

After rod reduction, locking of the cap within the coupling device isachieved by turning of a T-bar handle 10413. A threaded drive portion10421 is connected to the handle 10413 and configured to mate withthreading on the interior of the outer shaft 10101 so that turning ofthe handle causes advancement of the drive mechanism 10421 through theinterior of the outer shaft 10101. A drive shaft 10431 is rotatablecoupled to the threaded drive portion 10421 so that advancement of thedrive portion by turning of the handle linearly advances the drive shaft10431 without rotation. The end of the drive shaft 10431 is configuredto receive a cap member and drive the cap member into contact with acoupling member received in the head portion 10201 of the tool. Theabove structures are shown in an assembled state in FIG. 50.

The reducing mechanism 10301 of the tool is shown in greater detail inthe cross-sectional view of FIGS. 50 and 51. FIG. 50 illustrates themain components of the reducing mechanism: the access lever 10311, thereducer lever 10321, and the reducing shaft 10341. The reducer assemblymechanically operates kinematically as a four-bar linkage to shift thereducing shaft 10341 in order to advance the rod into the screwassembly.

The lever 10321 mechanically locks or bottoms out to prevent thepitching or crushing injury to the hand of the operator. The lever 10321is mounted to the outer shaft 10101 via a pivot pin which allows thelever 10321 to pivot on the outer shaft 10101. The lever 10321 providesthe operator with a mechanical advantage multiplied by the linkage 10331to linearly drive the reducing shaft 10341. The linkage 10331 isconnected to the reducing shaft 10341 by a pin 10323 to allow motion andforce to be transmitted from the lever 10321 to the reducing shaft 10341in a linear fashion, i.e. back and forth in a proximal or distaldirection.

The operator of the reducer inserter tool 10001 is able to place theirfingers underneath the lever 10321 through the operation of the accesslever 10311. The access lever 10311 deflects out of position to allowthe operator access to operate the lever 10321. The access lever 10311may be provided with Nitinol springs or rods placed within the springrecesses 10313 in order to assist in resilient deflection of the accesslever.

The reducing shaft 10341 interfaces with the rod at the distal shaft tip10313 shown in FIGS. 50, 51A, and 51B. The reducing shaft 10341 has abearing surface 10315 that interfaces and contacts the spinal rod. Thebearing surface may be contoured to match the exterior surface of therod. The rod is forced into position because the projections 10203 ofthe tool's head portion hold the yoke of the screw assembly while thebearing surface 10315 forces the rod into position.

The cap driving mechanism 10401 of the tool consists of four maincomponents shown in FIG. 50: the driver handle portion 10411, thethreaded portion 10421, the shaft portion 10431, and the coupling 10441.

The handle portion 10411 is the only visible portion of the cap drivingmechanism 10401 when the tool 10001 is assembled. The handle portion10411 may have hollowed out recesses 10413 in order to reduce weight ofthe tool 10001. Weight of the tool may be kept to a minimum to reduceinertia and the risk of impact force from the tool contacting thecervical region of the spine.

A threaded portion 10421 of the cap driving mechanism connects to thehandle portion 10411 and is complementary to threading on the outershaft member so that rotation of the handle and threaded portionadvances the cap driving mechanism toward the head of the tool. Thethreaded portion 10421 may have, for instance, double lead acmethreading that interfaces with the outer shaft 10101 to act as athreaded drive for the tool 10001. Double lead threading allows forquick action of the drive member 10401, i.e. reduced rotation of thehandle 10411 is required for linear driving of the cap into the screwassembly. The acme threading allows for extremely high loadings to beapplied to the threaded drive member 10401 yet allows for smooth andreliable operation.

An inner shaft portion 10431 for driving a cap member into a couplingdevice received in the tool head portion 10201 may be rotatably mountedto the threaded portion 10421. In one form, the threaded portion andshaft portion may be rotatably coupled by a pin 10433 attached to thethreaded portion and received in an annular channel in the exterior ofthe drive shaft. The pin 10433 transmits the linear motion of thethreaded portion 10421 to the shaft portion 10431. The shaft portion10431 then translates within the outer shaft 10101 and the reducingshaft 10341 without rotation. These structures are shown in greaterdetail in FIG. 52.

A coupling may be provided on the inner shaft 10431 to hold a cap memberof the coupling device thereto. The type of coupling will, of course,depend upon the type of cap member to be used. A coupling 10441 forconnection to a cap of the type shown in FIG. 27 (cap member 3070) or inFIG. 38 (cap member 5070) is located at the most distal end of the shaftportion 10431 as shown in FIGS. 51A-B. The coupling 10441 provides anon-rotatable connection to the cap of the screw assembly. The coupling10441 includes a snap fit post 10443, a cap bearing surface 10445, and adrive post 10447.

The snap fit posts 10443 will deflect inward and act as a cantileverspring to allow a snap fit connection to the central opening of a cap ofthe screw assembly. The pressure of the bearing surface 10445 on the capcreated by the cantilever spring action of the snap fit post 10443 keepsthe cap secured to the coupling 10441. Optionally, the cap can besecurely attached by the operator driving the cap into the coupling10441 with the assistance of a cap caddy (not shown). The cap locks intoplace and is supported by the drive post 10447 during the final lockingof the cap into the insert member. The cap may be properly orientedduring the final locking of the cap to the insert member by providingthe snap fit post 10443 with an elliptical shape matching an ellipticalopening in the center of the cap member.

When the handle 10411 is rotated and the cap is driven into the insertmember of the screw assembly, the coupling 10441 will maintain positionof the cap. The drive post 10447 then applies a compressive force to thehead of the cap to lock the cap into the insert member. The lockingforce of the insert member on the cap then secures the cap allowing thecap to disengage the snap fit post 10443 when the drive member 10401 isdriven in the proximal direction.

The reducer inserter tool 10001 can be manufactured by standard turning,milling, and Electro Discharge Machining (EDM). The reducer insertertool 10001 can be made from any suitable, structurally strong materials.The reducer inserter tool 10001 can be constructed of suitable materialswhich are compatible with the uses and environments into which thedevice will be utilized. Preferably, the reducer inserter tool 10001 isconstructed of metallic materials such as stainless steel or titanium.The reducer inserter tool 10001 may be sterilized through a number ofmethods, including the use of an autoclave, i.e. steam.

Once the screw assembly has been surgically implanted on the chosenvertebrae, then the spinal rod and cap are added with the assistance ofthe reducer inserter tool 10001. Typically, the drive member 10401 willbe extended to its furthest distal position by rotating the handle 10411in a clockwise manner. The reducer inserter tool 10001 may optionally bedriven into a cap in a cap caddy (not shown) to lock the cap to thecoupling 10441. The handle 10411 will typically then be rotated in acounter-clockwise manner to move the coupling 10441 and the cap in aproximal direction to keep the cap from mechanically interfering withthe reduction of the rod on the insert member.

The reduction process begins with placing the spinal rod within thescrew assembly. The rod may, for instance, snap temporarily into placefor temporary positioning. The screw assembly and rod are then capturedin the head of the reducer inserter. The lever 10321 will be pivoted tocause the reducer assembly 10301 to move to the proximal direction outof the way for further operation of the tool 10001. The head of thereducer inserter tool 10001 will then be placed around the screwassembly and spinal rod, shifting the coupling assembly into the accessport 10205 at the distal tip of the reducer inserter tool 10001. Thereducer lever 10321 will then be pivoted toward the handle of theinstrument to cause the reducer shaft 10341 to shift toward the distaldirection to force the spinal rod into the screw assembly. The lever10321 will lock into position to secure the rod into its final positionwithin the insert member of the screw assembly. In the types of couplingdevices shown in FIGS. 1-41, the reducer assembly may also shift theinsert core member with respect to the outer member held by the tool,thus locking the anchor member in place during the rod reductionprocess.

Since the reducer shaft is hollow, a cap member for locking the couplingassembly may be inserted therethrough while the reducer shaft holds therod in place within the coupling assembly. To insert the cap member, thehandle 10411 will be rotated, typically in a clockwise manner, to movethe coupling 10441 and the cap in the distal direction. The handle 10411is rotated until the drive member can no longer be rotated and thusfully inserting the cap into the insert member. The cap will then belocked into the insert member. The cap drive handle 10411 will then berotated in a counter-clockwise manner to disengage the coupling 10441from the cap. The lever is then pivoted to disengage the reducerassembly 10301. The entire assembled coupling device is freed from thedistal tip of the reducer inserter tool 10001 by moving the toolsideways so that the coupling device exists through the access port10205 to complete the rod reduction and cap insertion process.

Each of the above embodiments are only examples of the presentinventions, and the present inventions are not restricted to the aboveembodiments.

1. An assembly for securing an elongate member to the spine, theassembly comprising: an anchor member having a head portion with acenter and at least one curved surface portion and an attachment portioncoupled to the head portion; an insert member with a lower portionhaving walls forming a cavity for receiving the anchor head portion, thewalls configured to shift against the anchor head in order to fix theanchor head at an angular position with respect to the insert member;and an outer member having an inner surface defining an inner space forreceiving the insert member, the inner surface having at least a portionconfigured to shift the insert member lower portion walls against theanchor head; wherein the anchor attachment portion has a central axisand the center of the anchor head portion is offset from the attachmentportion central axis.
 2. The assembly of claim 1 further comprising: anupper portion of the insert member having arms to receive the elongatemember therebetween; and a rod lock member configured for linearinsertion between the outer member and at least one arm of the innermember in order to shift the at least one arm against the elongatemember.
 3. The assembly of claim 1 wherein the outer member has ashoulder portion with a tapered recess on an underside thereof.
 4. Theassembly of claim 1 further comprising: a surface contour of the outermember interior surface configured to shift the lower walls of theinsert portion toward one another to prevent the anchor head fromexiting the insert member interior space when the insert member isshifted to a first retention position within the interior space of theouter member, the surface contour further configured to shift the lowerwalls of the insert portion toward one another to frictionally lock theanchor head therebetween at a fixed angle when the insert member islinearly shifted to a second lock position; a protrusion located on theinsert member positioned and configured to engage a protrusion on theouter member when the insert member is shifted into the first retentionposition; the insert member protrusion and outer member protrusionconfigured to prevent movement of the insert member in a seconddirection after insertion of the insert member to the retention positionin a first direction.
 5. The assembly of claim 1, wherein the insertmember lower portion comprises first and second concentric wallsections, with the first wall section located above the second wallsection and configured to be wider than the second wall section.